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Anti-Lock Brake System (ABS) and Stability Control - System Operation and Component Description
System Operation
System Diagrams
Vacuum Boosted Brake System
Pump MotorHydraulic Valve SolenoidsHydraulic Pressure SensorGWMAWDPCMPSCMSIMABCMPAMIPMARCMAPIMIPCHVACWheel Speed SensorsBrake Vacuum SensorFD-CANHS-CAN1HS-CAN2HS-CAN3MS-CAN1SCCM
Electric Boosted Brake System
Pump MotorHydraulic Valve SolenoidsHydraulic Pressure SensorActuator Position SensorGWMAWDPCMPSCMCHCMSIMABCMPAMIPMARCMAPIMIPCHVACWheel Speed SensorsBrake Fluid Level SensorFD-CANHS-CAN1HS-CAN2HS-CAN3MS-CAN1SCCMATCMDDM
Network Message Chart
Module Network Input Messages - ABS Module
Anti-Lock Brake System (ABS)
On electric brake boosted vehicles, the ABS module, HCU and brake master cylinder are a single assembly called the EBB unit.
On vacuum brake boosted vehicles, the ABS module and HCU are a single assembly, while the vacuum booster and master cylinder are 2 separate assemblies.
The ABS module continuously monitors brake pedal input, lateral vehicle motion and the rotational speed of each wheel. On vacuum brake boosted vehicles, the PCM sends the brake pedal switch information to the ABS over the FD-CAN . On electric brake boosted brake vehicles, the EBB unit contains pedal stroke sensor and the ABS module directly reads the brake pedal input. On both brake booster type vehicles, the RCM sends lateral acceleration sensor information to the GWM over the HS-CAN2 which then relays the information to the ABS module over the FD-CAN . Wheel speed information is retrieved by the ABS module using 4 active wheel speed sensors.
When the ABS module detects an impending wheel lock during a braking event, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves inside the HCU or EBB unit while the hydraulic pump motor is activated. Once the affected wheel returns to the desired speed, the ABS module deactivates the hydraulic pump motor and the solenoid valves.
The ABS module has 2 self-test options, one uses a diagnostic scan tool and the other is carried out when the ABS module is initialized (ignition on). During either self-test the ABS module carries out a preliminary electrical check of the system sensors and activates the hydraulic pump motor for approximately one-half second. During this time, a buzzing or humming noise may be heard and a vibration may be felt in the brake pedal; this is a normal condition. During the module initialized self-test, the pump motor check is carried out at approximately 10 km/h (6 mph). Any malfunction detected in the system causes the ABS module to set a DTC , disable the ABS function and send a message over the FD-CAN to the GWM . The GWM then sends the message to the IPC over the HS-CAN3 to illuminate the ABS warning indicator. Diagnostic Trouble Codes (DTCs) which disable the ABS do not disable the base hydraulic power-assist braking system.
Electronic Brake Force Distribution (EBD)
On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module then uses wheel speed sensor inputs to evaluate rear wheel slip. Once the rear wheel slip exceeds a predetermined threshold, the ABS module closes the appropriate isolation valves to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels. If the rear wheel slip continues and exceeds a second predetermined threshold, the ABS module opens the dump valves to decrease the rear brake pressure and allow the rear wheels to recover. A slight bump sensation may be felt in the brake pedal when EBD is active.
If the ABS is disabled due to a DTC being present in the ABS module, EBD continues to function unless the DTC is for wheel speed sensors or the HCU . When EBD is disabled, the ABS warning indicator, the red brake warning indicator and stability-traction control indicator (sliding car icon) illuminate.
Electronic Parking Brake (EPB) Features
The ABS module is the controlling ECU for the electronic parking brake system and controls all parking brake features such as automatic drive away release. For additional information on the electronic parking brake system,
Refer to: Parking Brake - System Operation and Component Description (206-05 Parking Brake and Actuation, Description and Operation).
Emergency Brake Assist (EBA)
The EBA feature helps drivers in a severe braking event, such as an emergency, by applying the maximum possible braking force.
If the brake pedal is pressed very suddenly, the ABS module increases the hydraulic pressure to all of the brakes until the threshold for ABS intervention is reached. This generates the maximum braking power for the available traction. The ABS module monitors inputs from the brake pedal switch and from the pressure sensor within the HCU to check for sudden actuation of the brakes. With the brake pedal pressed, the ABS module triggers emergency braking if the rate of increase of hydraulic pressure exceeds the predetermined limit.
If the brake pedal is pressed so hard the ABS becomes active on the front wheels, the ABS module increases the pressure to the rear wheels up to the ABS intervention threshold.
EBA operation continues until the driver releases the brake pedal sufficiently for the hydraulic pressure in the system to drop below a specific threshold value. This threshold is saved in the ABS module.
Hill Start Assist
When the vehicle is stopped on an incline greater than approximately a 6% grade, the ABS module holds the brake pressure for approximately 1.5 seconds while the driver transitions from the brake pedal to the accelerator pedal. This is accomplished by monitoring several CAN messages and several sensors to determine if the vehicle is stopped and not parked, and if the vehicle is on an appropriate incline.
Supplemental Braking Assist
In addition to preventing wheel lock up during braking events, the ABS module also provides supplemental hydraulic brake assist through the use of the hydraulic pump motor and the solenoid valves. This is done in the event of a severe braking event, to maintain the distance gap set by the adaptive cruise control system or to assist with collision avoidance.
The ABS module continually monitors CAN messages and sensor inputs. When the messages or sensors indicate a severe braking event is about to occur or is occurring, the ABS module activates the hydraulic pump motor to assist with vehicle braking.
On vehicles equipped with adaptive cruise control, the CCM monitors the area forward of the vehicle and communicates the information to the IPMA over a LIN .
When an object enters this area and closes the distance gap set by the driver, the CCM sends a deceleration request to the IPMA . The IPMA then sends the message to the GWM over the HS-CAN2 which relays the message to the ABS module over the FD-CAN .
When the deceleration request message is received, the ABS module activates the hydraulic pump motor and solenoid valves to slow the vehicle down to maintain the distance gap set by the driver. Once the distance gap set by the driver is achieved, the CCM stops sending the deceleration request message and the ABS module deactivates the hydraulic pump motor and solenoid valves.
If the CCM determines the amount of braking provided by the ABS module is insufficient, the CCM sends a forward collision avoidance braking request message and warns the driver, both audibly and visually, through the use of the HUD . After receiving the braking request message, the ABS module waits for brake pedal input and, once received, applies maximum braking assist using the hydraulic pump motor and the solenoid valves.
For additional information on the adaptive cruise control system,
Refer to: Cruise Control - System Operation and Component Description (419-03B Cruise Control - Vehicles With: Adaptive Cruise Control, Description and Operation).
For additional information on the collision avoidance system,
AdvanceTrac
The AdvanceTrac system is comprised of the traction control and ESC features.
MyKey Interaction
Through the MyKey feature, traction control can be configured to be always on or to allow the driver to select the traction control function on or off. When the traction control function is configured to be always on and a MyKey restricted key is in use, the IPC ignores any requests made by the driver to disable the traction control function and does not send any traction control disable messages to the GWM . Refer to the Owner's Literature for additional information on the various MyKey settings.
Traction Control
The ABS module continuously monitors and compares the rotational speed of the drive wheels in relation to the non-driven wheels. When the drive wheels begin to spin faster than the non-driven wheels, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to eliminate the wheel slip and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a traction event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the traction event message, it flashes the stability-traction control indicator (sliding car icon).
Once the driven wheel speed returns to the desired speed, the ABS module deactivates the hydraulic pump motor and solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon). Once vehicle speed exceeds 100 km/h (62 mph), traction control is accomplished only through the PCM torque control.
On 4WD vehicles, the traction control system is disabled by the driver using the stability-traction control switch which is part of the AWD MSS . When the traction control switch is pressed, the ATCM sends a message to the ABS module over the FD-CAN and a message to the IPC through the GWM and over the HS-CAN3 . The ABS module takes no further action in regards to traction control until the driver presses the switch again in the same ignition cycle or until the ignition is cycled from OFF to ON. The IPC responds by illuminating the stability-traction control disabled indicator (sliding car OFF icon).
Disabling the traction control system is independent of ABS which cannot be disabled by the driver. The ABS module disables traction control if there are any wheel speed sensor or solenoid valve Diagnostic Trouble Codes (DTCs) present in the ABS module. Traction control is also disabled if there is a communication error between the ABS module and the PCM . When traction control is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Electronic Stability Control (ESC)
The ABS module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input and the yaw rate sensor input with the actual vehicle motion. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor and lateral accelerometer information to the ABS module over the HS-CAN2 through the GWM . If the ABS module determines from the inputs the vehicle is unable to travel in the intended direction, it modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to help stabilize the vehicle and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a vehicle stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon).
Once the vehicle instability has been corrected, the ABS module deactivates the hydraulic pump motor and solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon).
ESC does not operate with the transmission in REVERSE or with the transfer case in LOW range. The ABS module disables ESC if there are any wheel speed sensor, stability sensor or steering angle sensor Diagnostic Trouble Codes (DTCs) present in the ABS module. If there is a communication error between the ABS module and the PSCM or the ABS module and the RCM , ESC also is disabled. When ESC is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Stability-Traction Control Indicators
There are 2 stability-traction control indicators used to notify the vehicle occupants of stability and traction control concerns:
Refer to: Instrument Panel Cluster (IPC) - System Operation and Component Description (413-01 Instrumentation, Message Center and Warning Chimes, Description and Operation).
Stability Control Features
Curve Control
Curve control enhances the vehicle’s ability to follow the road when cornering severely or avoiding objects in the roadway. Curve control operates by reducing engine power and, if necessary, applying brakes to one or more of the wheels individually.
The ABS module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input, yaw rate sensor input and lateral accelerometer input with the actual vehicle motion. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor, lateral accelerometer and roll rate sensor information to the ABS module through the GWM over the HS-CAN2 . If the ABS module determines from the inputs the vehicle is becoming unstable, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to help stabilize the vehicle and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a vehicle stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon).
Once the vehicle instability has been corrected, the ABS module deactivates the hydraulic pump motor and the solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon).
RSC does not operate with the transmission in REVERSE or with the transfer case in LOW range. The ABS module disables RSC if there are any wheel speed sensor, stability sensor or steering angle sensor Diagnostic Trouble Codes (DTCs) present in the ABS module. If there is a communication error between the ABS module and the PSCM or the ABS module and the RCM , RSC also is disabled. When RSC is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Roll Stability Control (RSC)
Roll stability control aids in preventing rollovers by detecting the roll motion of the vehicle and the rate at which it changes by applying the brakes to one or more wheels individually.
The ABS module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input, yaw rate sensor input, lateral accelerometer input and roll sensor input with the actual vehicle motion. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor, lateral accelerometer and roll rate sensor information to the ABS module through the GWM over the HS-CAN2 . If the ABS module determines from the inputs the vehicle is becoming unstable, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to help stabilize the vehicle and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a vehicle stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon).
Once the vehicle instability has been corrected, the ABS module deactivates the hydraulic pump motor and the solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon).
RSC does not operate with the transmission in REVERSE, with the transfer case in LOW range or in Baja drive mode when stability controls have been disabled. The ABS module disables RSC if there are any wheel speed sensor, stability sensor or steering angle sensor Diagnostic Trouble Codes (DTCs) present in the ABS module. If there is a communication error between the ABS module and the PSCM or the ABS module and the RCM , RSC also is disabled. When RSC is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Torque Vector Control
Torque vectoring control applies the brakes on the inner driven wheel while in a curve for better traction to avoid an understeer or oversteer situation. Unlike ESC , torque vectoring control does not reduce engine RPM or slow the vehicle. It aids in controlling excessive wheel slip giving the vehicle improved cornering ability.
The ABS module continuously monitors and compares the rotational speed of the drive wheels in relation to the non-driven wheels. When torque vectoring control is needed, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module sends a stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the IPC receives the traction event message, it flashes the stability-traction control indicator (sliding car icon).
Once the stability event is over, the ABS module deactivates the hydraulic pump motor and solenoid valves, and stops sending the traction event and torque reduction messages. The IPC extinguishes the stability-traction control indicator (sliding car icon).
Trailer Sway Control
Trailer sway is the undesirable yaw force a trailer can apply to the towing vehicle. Trailer sway control is a unique function of the stability control system that uses steering wheel angle information and yaw rate information to determine if a trailer sway event is taking place. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor and lateral accelerometer information to the ABS module also over the HS-CAN2 through the GWM . If the ABS module determines from the inputs a trailer sway event is taking place, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while the activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to eliminate the trailer sway and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a trailer sway event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon) and displays TRAILER SWAY REDUCE SPEED in the message center.
Once the trailer sway has been corrected, the ABS module deactivates the hydraulic pump motor and the solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon) and stops displaying the trailer sway message in the message center. Trailer sway control only activates when vehicle speed is greater than 65 km/h (40 mph). Any malfunction disabling RSC also disables trailer sway control.
The driver can enable and disable the trailer sway control feature using the message center. For additional information, refer to the Owner's Literature.
Driving and Trail Features
Hill Descent Control
When the hill descent control switch on the AWD MSS is pressed, the ATCM sends a hill descent message to the ABS module over the FD-CAN . Once vehicle speed is between 5 km/h (3 mph) and 32 km/h (20 mph) and the transmission is in REVERSE or any forward gear, the ABS module uses the hydraulic pump motor and the solenoid valves to maintain the speed set by the driver. If the speed is increased or decreased outside of the operational window, the system remains active but descent speed cannot be set or maintained.
The hill descent control feature requires a cool down period after sustained use. The ABS module continually monitors the descent speed, angle of descent, pump motor run time and solenoid valve use. Once the ABS module determines a cool down period is needed, the module sends a message to the GWM over the FD-CAN . The GWM relays the message to the IPC over the HS-CAN3 to display HILL DESCENT CONTROL OFF SYSTEM COOLING in the message center.
Hill descent control has 3 modes of operation:
The selectable drive mode system optimizes driveability and comfort as well as maximizing traction while operating on different types of terrain. Drive modes are selected using the AWD MSS and the ATCM controls the drive mode selection. When a drive mode is selected, the ATCM sends the drive mode message to the ABS module over the FD-CAN . When the ABS module receives the message, it alters the intervention thresholds for the stability and traction control features based on the selected mode. The ABS module also sends the drive mode message out to several other modules. The following modules receive the message and respond by altering their operation as follows:
Trail Control
When the trail control switch is pressed, the ATCM sends a message to the ABS module over the FD-CAN . The trail control is now engaged and the indicator is illuminated gray until the system is activated.
To activate, the trail control feature requires the following conditions to be met:
The trail control feature transitions from active to enabled when any of the following occur:
Trail One Pedal Drive
When the trail one pedal drive button on the ATCM is pressed, the module sends a message to the ABS module over the FD-CAN . The trail one pedal drive is now engaged and the indicator is illuminated gray until the system is activated.
When trail one pedal drive is active, the indicator displays green in the instrument cluster. When the system is on but is unavailable or in standby mode, it displays grey.
To activate, the trail one pedal drive feature requires the following conditions to be met:
The following vehicle conditions exist while trail one pedal drive is active:
Trail Turn Assist
Trail turn assist can reduce the turning radius of your vehicle by applying the brakes to the inside rear wheel in low-speed, high steering-angle maneuvers.
While in 4WD HIGH or 4WD LOW, press the trail turn assist button to activate the feature. When the trail turn assist switch is pressed, the driveline chassis switch module sends a trail turn assist switch signal message to the ABS module over the FD-CAN . Trail turn assist is on at this time but is not activated until:
Component Description
Anti-Lock Brake System (ABS) Module
The ABS module is the ECU for the ABS and stability control systems. The ABS module monitors all sensor inputs and all CAN messages relating to ABS and stability control, then directly controls the solenoid valves and the hydraulic pump motor.
On vacuum brake boosted vehicles, the ABS module and HCU are a single assembly, while the vacuum booster and master cylinder are 2 separate assemblies.
On electric brake boosted vehicles, the ABS module, HCU and brake master cylinder are a single assembly called the EBB unit.
When a new ABS is installed, the module must be programmed with the current vehicle configuration information. For additional information on module programming,
Refer to: Module Configuration - System Operation and Component Description (418-01A Module Configuration, Description and Operation).
When an ABS or stability control fault has been corrected or a new component has been installed, the ABS module must be calibrated. The ABS Calibration procedure is required for the stability control sensors to learn the zero-position of the vehicle which means the vehicle must be on a level surface and not moving. The ABS Calibration procedure is carried out using a diagnostic scan tool.
All Wheel Drive (AWD) Mode Select Switch (MSS)
The AWD MSS is a multi-position, rotating switch and is part of the ATCM .
Brake Booster Vacuum Sensor
On vacuum brake boosted vehicles, the brake booster vacuum sensor is a piezoelectric device used by the ABS module to monitor the vacuum in the brake booster on vehicles equipped with a vacuum brake booster. The sensor is hardwired to the ABS module by 3 circuits. One circuit is for the 5 volt sensor supply, one circuit is for sensor ground and one circuit is for sensor output. The sensor output ranges from 0.3 volt to 4.7 volts, depending on the amount of vacuum in the booster.
Electric Brake Booster (EBB) Unit
Except for the brake fluid reservoir, the EBB unit is serviced as a single assembly and must NOT be disassembled.
The EBB unit contains the ABS module, solenoid valves, pressure sensor and hydraulic pump motor; the EBB unit also takes the place of the brake master cylinder, the vacuum booster, the HCU and the brake pedal switch.
When a new EBB assembly is installed, the ABS module must be programmed with the current vehicle configuration information. For additional information on module programming,
Refer to: Module Configuration - System Operation and Component Description (418-01A Module Configuration, Description and Operation).
When an ABS or stability control fault has been corrected or a new component has been installed, the ABS module must be calibrated using the ABS Calibration routine found in the diagnostic scan tool. ABS Calibration is required for the stability control sensors to learn the zero-position of the vehicle which means the vehicle must be on a level surface and not moving.
Hill Descent Control Switch
The hill descent control switch is a single-pole, momentary-contact switch and is part of the ATCM .
Hydraulic Control Unit (HCU)
Vehicles equipped with a vacuum brake booster are also equipped with an HCU .
The HCU contains the solenoid valves, the hydraulic pump motor and the pressure sensor used by the ABS for the ABS and stability control systems. While the ABS module can be serviced separately from the HCU , a new HCU comes with a new ABS module.
Stability Control Sensors
The stability control sensors for the traction control and stability control functions consist of the yaw rate sensor, lateral accelerometer, longitudinal accelerometer and roll rate sensor. The sensors are housed in the RCM which sends sensor information to the ABS module over the HS-CAN2 . If any of the sensors are defective, a new RCM must be installed.
Trail Control Switch
The trail control switch is a single-pole, momentary-contact switch and is part of the ATCM .
Wheel Speed Sensors
All 4 wheel speed sensors are active (magneto resistive) sensors that operate on the Hall-effect principle to generate a square wave signal proportional to the rotational speed of the wheel. Because these are active sensors, receiving voltage from the ABS module and sending a varying voltage back to the ABS module, they are able to detect much lower rotational speeds than passive (magnetic inductive) sensors. Each wheel speed sensor is connected to the ABS module by 2 circuits. One circuit provides voltage for sensor operation and the other circuit provides sensor input to the ABS module.
The front wheel speed sensors are mounted on the front wheel hub and are serviced separately.
The rear wheel speed sensors are mounted on the axle flange at the brake dust shield and can be serviced separately.
Wheel Speed Sensor Encoders
The wheel speed sensor encoders are magnetized, toothed rings used to create a Hall-effect switch when combined with the wheel speed sensor. The front wheel speed sensor encoders are integrated into the wheel bearing and hub assembly and are serviced with the assembly. The rear wheel speed sensor encoders are pressed onto the axle shaft and are serviced with the axle shaft.
System Operation
System Diagrams
Vacuum Boosted Brake System
Pump MotorHydraulic Valve SolenoidsHydraulic Pressure SensorGWMAWDPCMPSCMSIMABCMPAMIPMARCMAPIMIPCHVACWheel Speed SensorsBrake Vacuum SensorFD-CANHS-CAN1HS-CAN2HS-CAN3MS-CAN1SCCM
Electric Boosted Brake System
Pump MotorHydraulic Valve SolenoidsHydraulic Pressure SensorActuator Position SensorGWMAWDPCMPSCMCHCMSIMABCMPAMIPMARCMAPIMIPCHVACWheel Speed SensorsBrake Fluid Level SensorFD-CANHS-CAN1HS-CAN2HS-CAN3MS-CAN1SCCMATCMDDM
Network Message Chart
Module Network Input Messages - ABS Module
| Broadcast Message | Originating Module | Message Purpose |
|---|---|---|
| Accelerator pedal position | PCM | The ABS module uses accelerator pedal position information for correct operation of the ABS , traction control, ESC , RSC and the automatic release feature of the electronic parking brake system. |
| Adaptive cruise control braking deceleration | IPMA | This message is sent to the GWM and then to the ABS module. This message is used to request vehicle deceleration by the ABS module to maintain the distance gap set by the driver for the adaptive cruise control system. |
| Adaptive cruise control brake torque request | IPMA | This message is sent to the GWM and then to the ABS module. Informs the ABS module of the amount of braking required to maintain the distance gap set by the driver for the adaptive cruise control system. |
| Adaptive cruise control precharge request | IPMA | This message is sent to the GWM and then to the ABS module. This message is used to request precharging of the hydraulic brake system in preparation of a adaptive cruise control braking event. |
| AWD locking status | AWD control module | Informs the ABS module of the current differential locked status; no fault, unspecified fault, differential failed open and differential failed closed. The ABS module requests differential unlocking during traction control, ESC and RSC operations. |
| AWD locking torque | AWD control module | Informs the ABS module of the current amount of torque being applied to the differential. The ABS module requests differential unlocking during traction control, ESC and RSC operations. |
| AWD range | AWD control module | Informs the ABS module of the current AWD range. The ABS module modifies the selectable drive mode operating parameters based on the current AWD range. |
| AWD service required | AWD control module | Informs the ABS module of the current AWD system operating status. The ABS module modifies the selectable drive mode operating parameters based on the current AWD status. |
| Ambient air temperature | PCM | Informs the ABS module of the current ambient air temperature. The ABS module uses this information for system diagnostics and DTC setting conditions. |
| Brake pedal applied | PCM | Informs the ABS module the driver has pressed the brake pedal. This message is also used by the ABS module for self-diagnostic purposes. |
| Braking request | IPMA | This message is sent to the GWM and then to the ABS module. This message is an adaptive cruise control braking request from the IPMA . |
| Clutch pedal position | PCM | The ABS module uses clutch pedal position information for correct operation of the ABS , traction control, and the stability control features.. |
| Collision mitigation by braking deceleration | IPMA | This message is sent to the GWM and then to the ABS module. This message is used to request vehicle deceleration by the ABS module for the collision avoidance system. |
| Collision mitigation by braking precharge request | IPMA | This message is sent to the GWM and then to the ABS module. This message is sent to the GWM and then to the ABS module. This message is used to request precharging of the hydraulic brake system in preparation of a severe braking event. |
| Cruise control status | PCM | Informs the ABS module of the current cruise control system status; off, denied, standby denied, standby active que assist, active or undefined. |
| Differential locking status | AWD control module | Informs the ABS module of the current front and rear differential locking status. The ABS module modifies the selectable drive mode operating parameters based on the current differential locking status. |
| Door ajar status | DDM | Informs the ABS module of the current door ajar status. The ABS module resets the parameters used for the stability control features when a door is opened. The message is also used for the Trail Control, Trail One-Pedal Drive and EPB automatic release feature. |
| Driven wheel direction | PCM | Provides the ABS module with the current direction of the driven wheels. This information is used for traction control and stability control purposes. |
| Driven wheel torque | PCM | Provides the ABS module with the current torque output at the driven wheels. This information is used for traction control and stability control purposes. |
| Driver seatbelt buckle status | RCM | Informs the ABS module of the current driver seatbelt buckle status. The message is used for the Trail Control, Trail One-Pedal Drive and EPB automatic release feature. |
| Engine disable status | PCM | Informs the ABS module the engine is currently disabled or enabled due to the stop-start system. |
| Engine RPM | PCM | Provides the ABS module with the current engine RPM . This information is used for traction control and stability control purposes. |
| Gear lever position | PCM | Provides the ABS module with the current transmission gear lever position, this is used for the hill start assist system, the ESC and the RSC systems. The hill start assist system operates in forward and reverse gears. The ESC and RSC systems do not operate when the transmission is in REVERSE. The message is also used for the electronic parking brake automatic release feature. |
| Hill descent control request | IPC ( 2WD vehicles) | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current, driver selected mode for the hill descent control system; off or on. |
| Hill descent control request | AWD control module ( 4WD vehicles) | Provides the ABS module with the current, driver selected mode for the hill descent control system; off or on. |
| Hill start assist request | IPC | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current, driver selected mode for the hill start assist system; off, auto or manual. |
| Ignition key type | BCM | This message is sent to the GWM and then to the ABS module. Informs the ABS module of the current ignition key type; standard or MyKey. The ABS modifies operating parameters if a restricted MyKey is used. |
| Ignition status | BCM | This message is sent to the GWM and then to the ABS module. Informs the ABS module of the current ignition status; off, accessory, run, start, unknown or invalid. |
| Odometer master value | IPC | This message is sent to the GWM and then to the ABS module. Informs the ABS module of the current odometer value in kilometers. |
| Parking brake apply request | BCM | This message is sent to the GWM and then to the ABS module. This message is a request for parking brake application from the BCM for the EPB auto hold feature. |
| Parking brake apply request | PAM | This message is sent to the GWM and then to the ABS module. This message is a request for parking brake application from the PAM for the active park assist feature. |
| PATS start request target command | PCM | Provides the ABS module with the challenge and password for anti-theft vehicle starting. During vehicle starting, the PCM and the ABS module exchange information to make sure the vehicle is being started correctly. |
| PATS start request target status | PCM | Informs the ABS module of the current anti-theft start request status; disabled, enabled motive start, enabled non-motive start, disabled reset. |
| Powertrain status | PCM | Provides the ABS module with the current engine status; engine off, engine on or engine auto stopped. |
| RCM serial number | RCM | This message is sent to the GWM and then to the ABS module. The ABS module stores the RCM serial number and verifies the serial number when the vehicle is started or the ignition is set to RUN or ACC. Over time, the ABS module learns the offset of the sensors inside the RCM . When a new serial number is found when the ABS Calibration procedure is carried out using a diagnostic scan tool, the ABS module resets the offset number learned for ESC and RSC . |
| Restraint system impact event status | RCM | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current SRS impact event status; normal, threshold 1 exceeded, threshold 2 exceeded or invalid. |
| Selectable drive mode request | APIM ( 2WD vehicles) | Provides the ABS module with the driver selected drive mode request. |
| Selectable drive mode request | AWD control module ( 4WD vehicles) | Provides the ABS module with the driver selected drive mode request. |
| Selectable drive mode suspension status | CHCM | Provides the ABS module with the current selectable drive mode status of the suspension system. |
| Stabilizer bar disconnect status | CHCM | Informs the ABS module of the current stabilizer bar disconnect system status. |
| Steering angle sensor data | PSCM | Several steering angle messages are sent to the ABS module from the PSCM . These messages include steering angle sensor status, steering wheel angle and steering wheel rotation count. The ABS module uses the steering angle sensor data for stability control feature operation. |
| Steering column torque | PSCM | Provides the ABS module with the current amount of torque being applied to the steering wheel by the driver. The ABS module uses this information for stability control feature operation. |
| Traction control status | AWD control module ( 4WD vehicles) | Informs the ABS module of the current traction control system status; active or inactive. |
| Traction control status | IPC ( 2WD vehicles) | This message is sent to the GWM and then to the ABS module. Informs the ABS module of the current traction control system status; active or inactive. |
| Traction control switch | DLSM (Driveline Switch Module) (4WD vehicles) | Informs the ABS module of the current traction control switch status; pressed or not pressed. |
| Trail control system status | AWD control module | Informs the ABS module of the current vehicle trail control system status. |
| Trailer backup assist status | PSCM | Informs the ABS module of the current vehicle trailer sway configuration; active, inactive or setup. |
| Trailer brake status | TRM | Informs the ABS module a trailer is connected or disconnected to the vehicle. |
| Trailer sway configuration | IPC | This message is sent to the GWM and then to the ABS module. Informs the ABS module of the current vehicle trailer sway configuration. |
| Trail turn assist request | Driveline Chassis Switch Module | Informs the ABS module of the current vehicle trail control system status. |
| Transmission in neutral | PCM | Informs the ABS module when the transmission has been placed in neutral mode. The ABS module modifies the operating parameters for stability control when the transmission is in neutral mode. |
| Transmission shift active | PCM | Informs the ABS module when the transmission is shifting gears. This information is used for stability control purposes. |
| Transmission in reverse | PCM | Informs the ABS module when the transmission is in REVERSE. The ESC and RSC systems do not operate when the transmission is in REVERSE. |
| Vehicle configuration data | BCM | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current optional and configured items such as tire size, axle ratio, manual or automatic transaxle, keyless entry and VIN . |
| Vehicle lateral acceleration data | RCM | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current vehicle lateral acceleration information and whether or not the information is valid. |
| Vehicle longitudinal acceleration data | RCM | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current vehicle longitudinal acceleration information and whether or not the information is valid. |
| Vehicle roll rate data | RCM | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current vehicle roll rate information and whether or not the information is valid. |
| Vehicle speed data | PCM | Provides the ABS module with the current vehicle speed. |
| Vehicle yaw data | RCM | This message is sent to the GWM and then to the ABS module. Provides the ABS module with the current vehicle yaw information and whether or not the information is valid. |
Anti-Lock Brake System (ABS)
On electric brake boosted vehicles, the ABS module, HCU and brake master cylinder are a single assembly called the EBB unit.
On vacuum brake boosted vehicles, the ABS module and HCU are a single assembly, while the vacuum booster and master cylinder are 2 separate assemblies.
The ABS module continuously monitors brake pedal input, lateral vehicle motion and the rotational speed of each wheel. On vacuum brake boosted vehicles, the PCM sends the brake pedal switch information to the ABS over the FD-CAN . On electric brake boosted brake vehicles, the EBB unit contains pedal stroke sensor and the ABS module directly reads the brake pedal input. On both brake booster type vehicles, the RCM sends lateral acceleration sensor information to the GWM over the HS-CAN2 which then relays the information to the ABS module over the FD-CAN . Wheel speed information is retrieved by the ABS module using 4 active wheel speed sensors.
When the ABS module detects an impending wheel lock during a braking event, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves inside the HCU or EBB unit while the hydraulic pump motor is activated. Once the affected wheel returns to the desired speed, the ABS module deactivates the hydraulic pump motor and the solenoid valves.
The ABS module has 2 self-test options, one uses a diagnostic scan tool and the other is carried out when the ABS module is initialized (ignition on). During either self-test the ABS module carries out a preliminary electrical check of the system sensors and activates the hydraulic pump motor for approximately one-half second. During this time, a buzzing or humming noise may be heard and a vibration may be felt in the brake pedal; this is a normal condition. During the module initialized self-test, the pump motor check is carried out at approximately 10 km/h (6 mph). Any malfunction detected in the system causes the ABS module to set a DTC , disable the ABS function and send a message over the FD-CAN to the GWM . The GWM then sends the message to the IPC over the HS-CAN3 to illuminate the ABS warning indicator. Diagnostic Trouble Codes (DTCs) which disable the ABS do not disable the base hydraulic power-assist braking system.
Electronic Brake Force Distribution (EBD)
On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module then uses wheel speed sensor inputs to evaluate rear wheel slip. Once the rear wheel slip exceeds a predetermined threshold, the ABS module closes the appropriate isolation valves to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels. If the rear wheel slip continues and exceeds a second predetermined threshold, the ABS module opens the dump valves to decrease the rear brake pressure and allow the rear wheels to recover. A slight bump sensation may be felt in the brake pedal when EBD is active.
If the ABS is disabled due to a DTC being present in the ABS module, EBD continues to function unless the DTC is for wheel speed sensors or the HCU . When EBD is disabled, the ABS warning indicator, the red brake warning indicator and stability-traction control indicator (sliding car icon) illuminate.
Electronic Parking Brake (EPB) Features
The ABS module is the controlling ECU for the electronic parking brake system and controls all parking brake features such as automatic drive away release. For additional information on the electronic parking brake system,
Refer to: Parking Brake - System Operation and Component Description (206-05 Parking Brake and Actuation, Description and Operation).
Emergency Brake Assist (EBA)
The EBA feature helps drivers in a severe braking event, such as an emergency, by applying the maximum possible braking force.
If the brake pedal is pressed very suddenly, the ABS module increases the hydraulic pressure to all of the brakes until the threshold for ABS intervention is reached. This generates the maximum braking power for the available traction. The ABS module monitors inputs from the brake pedal switch and from the pressure sensor within the HCU to check for sudden actuation of the brakes. With the brake pedal pressed, the ABS module triggers emergency braking if the rate of increase of hydraulic pressure exceeds the predetermined limit.
If the brake pedal is pressed so hard the ABS becomes active on the front wheels, the ABS module increases the pressure to the rear wheels up to the ABS intervention threshold.
EBA operation continues until the driver releases the brake pedal sufficiently for the hydraulic pressure in the system to drop below a specific threshold value. This threshold is saved in the ABS module.
Hill Start Assist
When the vehicle is stopped on an incline greater than approximately a 6% grade, the ABS module holds the brake pressure for approximately 1.5 seconds while the driver transitions from the brake pedal to the accelerator pedal. This is accomplished by monitoring several CAN messages and several sensors to determine if the vehicle is stopped and not parked, and if the vehicle is on an appropriate incline.
- On vacuum brake boosted vehicles, the brake pedal message sent by the PCM and the wheel speed sensor inputs allow the ABS module to determine the vehicle has come to a complete stop.
- On electric brake boosted vehicles, the brake pedal and wheel speed sensor inputs allow the ABS module to determine the vehicle has come to a complete stop.
- The transmission selector lever message sent by the PCM informs the ABS module the vehicle is not parked.
- The stability sensor messages sent by the RCM enable the ABS module to determine if the vehicle is on an appropriate incline.
Supplemental Braking Assist
In addition to preventing wheel lock up during braking events, the ABS module also provides supplemental hydraulic brake assist through the use of the hydraulic pump motor and the solenoid valves. This is done in the event of a severe braking event, to maintain the distance gap set by the adaptive cruise control system or to assist with collision avoidance.
The ABS module continually monitors CAN messages and sensor inputs. When the messages or sensors indicate a severe braking event is about to occur or is occurring, the ABS module activates the hydraulic pump motor to assist with vehicle braking.
On vehicles equipped with adaptive cruise control, the CCM monitors the area forward of the vehicle and communicates the information to the IPMA over a LIN .
When an object enters this area and closes the distance gap set by the driver, the CCM sends a deceleration request to the IPMA . The IPMA then sends the message to the GWM over the HS-CAN2 which relays the message to the ABS module over the FD-CAN .
When the deceleration request message is received, the ABS module activates the hydraulic pump motor and solenoid valves to slow the vehicle down to maintain the distance gap set by the driver. Once the distance gap set by the driver is achieved, the CCM stops sending the deceleration request message and the ABS module deactivates the hydraulic pump motor and solenoid valves.
If the CCM determines the amount of braking provided by the ABS module is insufficient, the CCM sends a forward collision avoidance braking request message and warns the driver, both audibly and visually, through the use of the HUD . After receiving the braking request message, the ABS module waits for brake pedal input and, once received, applies maximum braking assist using the hydraulic pump motor and the solenoid valves.
For additional information on the adaptive cruise control system,
Refer to: Cruise Control - System Operation and Component Description (419-03B Cruise Control - Vehicles With: Adaptive Cruise Control, Description and Operation).
For additional information on the collision avoidance system,
AdvanceTrac
The AdvanceTrac system is comprised of the traction control and ESC features.
MyKey Interaction
Through the MyKey feature, traction control can be configured to be always on or to allow the driver to select the traction control function on or off. When the traction control function is configured to be always on and a MyKey restricted key is in use, the IPC ignores any requests made by the driver to disable the traction control function and does not send any traction control disable messages to the GWM . Refer to the Owner's Literature for additional information on the various MyKey settings.
Traction Control
The ABS module continuously monitors and compares the rotational speed of the drive wheels in relation to the non-driven wheels. When the drive wheels begin to spin faster than the non-driven wheels, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to eliminate the wheel slip and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a traction event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the traction event message, it flashes the stability-traction control indicator (sliding car icon).
Once the driven wheel speed returns to the desired speed, the ABS module deactivates the hydraulic pump motor and solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon). Once vehicle speed exceeds 100 km/h (62 mph), traction control is accomplished only through the PCM torque control.
On 4WD vehicles, the traction control system is disabled by the driver using the stability-traction control switch which is part of the AWD MSS . When the traction control switch is pressed, the ATCM sends a message to the ABS module over the FD-CAN and a message to the IPC through the GWM and over the HS-CAN3 . The ABS module takes no further action in regards to traction control until the driver presses the switch again in the same ignition cycle or until the ignition is cycled from OFF to ON. The IPC responds by illuminating the stability-traction control disabled indicator (sliding car OFF icon).
Disabling the traction control system is independent of ABS which cannot be disabled by the driver. The ABS module disables traction control if there are any wheel speed sensor or solenoid valve Diagnostic Trouble Codes (DTCs) present in the ABS module. Traction control is also disabled if there is a communication error between the ABS module and the PCM . When traction control is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Electronic Stability Control (ESC)
The ABS module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input and the yaw rate sensor input with the actual vehicle motion. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor and lateral accelerometer information to the ABS module over the HS-CAN2 through the GWM . If the ABS module determines from the inputs the vehicle is unable to travel in the intended direction, it modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to help stabilize the vehicle and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a vehicle stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon).
Once the vehicle instability has been corrected, the ABS module deactivates the hydraulic pump motor and solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon).
ESC does not operate with the transmission in REVERSE or with the transfer case in LOW range. The ABS module disables ESC if there are any wheel speed sensor, stability sensor or steering angle sensor Diagnostic Trouble Codes (DTCs) present in the ABS module. If there is a communication error between the ABS module and the PSCM or the ABS module and the RCM , ESC also is disabled. When ESC is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Stability-Traction Control Indicators
There are 2 stability-traction control indicators used to notify the vehicle occupants of stability and traction control concerns:
- Stability-traction control indicator (sliding car icon) - this indicator notifies the vehicle occupants the stability or traction control system is operating by flashing once every 2 seconds.
- Stability-traction control disabled indicator (sliding car OFF icon) - this indicator notifies the vehicle occupants the stability or traction control has been disabled by remaining illuminated during vehicle operation.
Refer to: Instrument Panel Cluster (IPC) - System Operation and Component Description (413-01 Instrumentation, Message Center and Warning Chimes, Description and Operation).
Stability Control Features
Curve Control
Curve control enhances the vehicle’s ability to follow the road when cornering severely or avoiding objects in the roadway. Curve control operates by reducing engine power and, if necessary, applying brakes to one or more of the wheels individually.
The ABS module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input, yaw rate sensor input and lateral accelerometer input with the actual vehicle motion. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor, lateral accelerometer and roll rate sensor information to the ABS module through the GWM over the HS-CAN2 . If the ABS module determines from the inputs the vehicle is becoming unstable, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to help stabilize the vehicle and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a vehicle stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon).
Once the vehicle instability has been corrected, the ABS module deactivates the hydraulic pump motor and the solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon).
RSC does not operate with the transmission in REVERSE or with the transfer case in LOW range. The ABS module disables RSC if there are any wheel speed sensor, stability sensor or steering angle sensor Diagnostic Trouble Codes (DTCs) present in the ABS module. If there is a communication error between the ABS module and the PSCM or the ABS module and the RCM , RSC also is disabled. When RSC is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Roll Stability Control (RSC)
Roll stability control aids in preventing rollovers by detecting the roll motion of the vehicle and the rate at which it changes by applying the brakes to one or more wheels individually.
The ABS module continuously monitors the vehicle motion relative to the intended course. This is done by using sensors to compare the steering wheel input, yaw rate sensor input, lateral accelerometer input and roll sensor input with the actual vehicle motion. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor, lateral accelerometer and roll rate sensor information to the ABS module through the GWM over the HS-CAN2 . If the ABS module determines from the inputs the vehicle is becoming unstable, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to help stabilize the vehicle and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a vehicle stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon).
Once the vehicle instability has been corrected, the ABS module deactivates the hydraulic pump motor and the solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon).
RSC does not operate with the transmission in REVERSE, with the transfer case in LOW range or in Baja drive mode when stability controls have been disabled. The ABS module disables RSC if there are any wheel speed sensor, stability sensor or steering angle sensor Diagnostic Trouble Codes (DTCs) present in the ABS module. If there is a communication error between the ABS module and the PSCM or the ABS module and the RCM , RSC also is disabled. When RSC is disabled, the ABS module sends a message to the GWM over the FD-CAN . The GWM relays this message to the IPC over the HS-CAN3 to illuminate the stability-traction control indicator (sliding car icon).
Torque Vector Control
Torque vectoring control applies the brakes on the inner driven wheel while in a curve for better traction to avoid an understeer or oversteer situation. Unlike ESC , torque vectoring control does not reduce engine RPM or slow the vehicle. It aids in controlling excessive wheel slip giving the vehicle improved cornering ability.
The ABS module continuously monitors and compares the rotational speed of the drive wheels in relation to the non-driven wheels. When torque vectoring control is needed, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while activating the hydraulic pump motor. At the same time, the ABS module sends a stability event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the IPC receives the traction event message, it flashes the stability-traction control indicator (sliding car icon).
Once the stability event is over, the ABS module deactivates the hydraulic pump motor and solenoid valves, and stops sending the traction event and torque reduction messages. The IPC extinguishes the stability-traction control indicator (sliding car icon).
Trailer Sway Control
Trailer sway is the undesirable yaw force a trailer can apply to the towing vehicle. Trailer sway control is a unique function of the stability control system that uses steering wheel angle information and yaw rate information to determine if a trailer sway event is taking place. The PSCM sends the steering wheel angle information to the ABS module over the FD-CAN . The RCM sends yaw rate sensor and lateral accelerometer information to the ABS module also over the HS-CAN2 through the GWM . If the ABS module determines from the inputs a trailer sway event is taking place, the ABS module modulates brake pressure to the appropriate brake calipers by opening and closing the appropriate solenoid valves while the activating the hydraulic pump motor. At the same time, the ABS module calculates how much engine torque reduction is required to eliminate the trailer sway and sends this torque reduction message to the PCM over the FD-CAN . The ABS module also sends a trailer sway event message to the GWM over the FD-CAN which relays this message to the IPC over the HS-CAN3 . When the PCM receives the torque reduction message, it adjusts engine timing and decreases fuel injector pulses to reduce the engine torque to the requested level. When the IPC receives the vehicle stability event message, it flashes the stability-traction control indicator (sliding car icon) and displays TRAILER SWAY REDUCE SPEED in the message center.
Once the trailer sway has been corrected, the ABS module deactivates the hydraulic pump motor and the solenoid valves, and stops sending the traction event and torque reduction messages. The PCM returns engine timing and fuel injectors to normal operation and the IPC extinguishes the stability-traction control indicator (sliding car icon) and stops displaying the trailer sway message in the message center. Trailer sway control only activates when vehicle speed is greater than 65 km/h (40 mph). Any malfunction disabling RSC also disables trailer sway control.
The driver can enable and disable the trailer sway control feature using the message center. For additional information, refer to the Owner's Literature.
Driving and Trail Features
Hill Descent Control
When the hill descent control switch on the AWD MSS is pressed, the ATCM sends a hill descent message to the ABS module over the FD-CAN . Once vehicle speed is between 5 km/h (3 mph) and 32 km/h (20 mph) and the transmission is in REVERSE or any forward gear, the ABS module uses the hydraulic pump motor and the solenoid valves to maintain the speed set by the driver. If the speed is increased or decreased outside of the operational window, the system remains active but descent speed cannot be set or maintained.
The hill descent control feature requires a cool down period after sustained use. The ABS module continually monitors the descent speed, angle of descent, pump motor run time and solenoid valve use. Once the ABS module determines a cool down period is needed, the module sends a message to the GWM over the FD-CAN . The GWM relays the message to the IPC over the HS-CAN3 to display HILL DESCENT CONTROL OFF SYSTEM COOLING in the message center.
Hill descent control has 3 modes of operation:
- At speeds below 32 km/h (20 mph): when the hill descent control switch is pressed and conditions are correct for hill descent activation, the hill descent control system is enabled. The hill descent indicator illuminates solidly and the message center indicates hill descent control is active.
- At speeds below 32 km/h (20 mph): when the hill descent control switch is pressed and conditions are not correct for hill descent activation; the hill descent control system is enabled, the hill descent control indicator illuminates solidly and a message is displayed in the message center indicating the reason hill descent is not active.
- At speeds above 32 km/h (20 mph): when the hill descent control switch is pressed, the hill descent control system is not enabled and the hill descent control indicator does not illuminate. Once the vehicle slows to below 32 km/h (20 mph), the hill descent control switch must be pressed again to enable the hill descent control system.
The selectable drive mode system optimizes driveability and comfort as well as maximizing traction while operating on different types of terrain. Drive modes are selected using the AWD MSS and the ATCM controls the drive mode selection. When a drive mode is selected, the ATCM sends the drive mode message to the ABS module over the FD-CAN . When the ABS module receives the message, it alters the intervention thresholds for the stability and traction control features based on the selected mode. The ABS module also sends the drive mode message out to several other modules. The following modules receive the message and respond by altering their operation as follows:
- AWD module: automatically engages and disengages specific 4WD modes and raises or lowers torque output based on the selected mode.
- PCM : adjusts throttle response and gear changes to enhance powertrain response based on the selected mode.
- PSCM : adjusts steering effort and feel based on the selected mode.
- Baja: For high speed off-road driving. Baja mode optimizes the throttle control for better response and torque delivery.
- Eco: For efficient driving. This mode helps deliver maximum fuel efficiency and helps to increase driving range.
- Mud / Ruts: For off-road driving. This mode enhances vehicle performance to traverse muddy, rutted or uneven terrains.
- Normal: For everyday driving. This mode is a perfect balance of excitement, comfort and convenience. This is the default mode after each ignition cycle.
- Rock Crawl: For off-road driving and optimum rock-climbing ability. Rock crawl mode optimizes the throttle and transmission response to provide additional control of the vehicle.
- Sand: For off-road driving on soft, dry sand or deep snow.
- Slippery: For less than ideal road conditions such as snow or ice covered roads. Slippery mode lowers throttle response and optimizes shifting for slippery surfaces.
- Sport: For sporty driving with improved performance handling and response. This mode increases accelerator pedal response and provides a sportier steering feel. The powertrain system holds onto lower gears longer, allowing the vehicle to accelerate faster.
Trail Control
When the trail control switch is pressed, the ATCM sends a message to the ABS module over the FD-CAN . The trail control is now engaged and the indicator is illuminated gray until the system is activated.
To activate, the trail control feature requires the following conditions to be met:
- Driver door is closed or the driver door is not present but the driver seatbelt is buckled.
- Parking brake is released.
- Vehicle speed is less than 31 km/h (20 mph) with the transfer case in high range.
- Vehicle speed is less than 15 km/h (10 mph) with the transfer case in low range.
- Vehicle speed is less than 8 km/h (5 mph) with the transmission in REVERSE.
The trail control feature transitions from active to enabled when any of the following occur:
- The CNCL-RES button is pressed.
- The transmission is shifted into PARK.
- The driver door is opened or the driver door is not present and the driver seatbelt is unbuckled.
- The parking brake is applied.
- A substantial service brake pedal application occurs.
Trail One Pedal Drive
When the trail one pedal drive button on the ATCM is pressed, the module sends a message to the ABS module over the FD-CAN . The trail one pedal drive is now engaged and the indicator is illuminated gray until the system is activated.
When trail one pedal drive is active, the indicator displays green in the instrument cluster. When the system is on but is unavailable or in standby mode, it displays grey.
To activate, the trail one pedal drive feature requires the following conditions to be met:
- The transfer case is in 4WD HIGH or 4WD LOW.
- Cruise control is OFF.
- Trail control is OFF.
- Vehicle speed is less than 48 km/h (30 mph).
The following vehicle conditions exist while trail one pedal drive is active:
- Shifting the transmission into DRIVE or REVERSE does not cause the vehicle to move.
- The brake pedal can still be pressed to increase braking. This does not turn the system off.
- Trail one pedal drive may apply the parking brake if the vehicle is not moving and the transmission is not in PARK.
- The trail one pedal drive button on the ATCM is pressed again.
- Shifting the transfer case to a driveline mode other than 4WD HIGH or 4WD LOW.
- Vehicle speed exceeds 68 km/h (42 mph).
Trail Turn Assist
Trail turn assist can reduce the turning radius of your vehicle by applying the brakes to the inside rear wheel in low-speed, high steering-angle maneuvers.
While in 4WD HIGH or 4WD LOW, press the trail turn assist button to activate the feature. When the trail turn assist switch is pressed, the driveline chassis switch module sends a trail turn assist switch signal message to the ABS module over the FD-CAN . Trail turn assist is on at this time but is not activated until:
- Vehicle speed is less than 19 km/h (12 mph).
- Rear differential is fully unlocked.
- Steering wheel is almost fully turned to the left or right.
Component Description
Anti-Lock Brake System (ABS) Module
The ABS module is the ECU for the ABS and stability control systems. The ABS module monitors all sensor inputs and all CAN messages relating to ABS and stability control, then directly controls the solenoid valves and the hydraulic pump motor.
On vacuum brake boosted vehicles, the ABS module and HCU are a single assembly, while the vacuum booster and master cylinder are 2 separate assemblies.
On electric brake boosted vehicles, the ABS module, HCU and brake master cylinder are a single assembly called the EBB unit.
When a new ABS is installed, the module must be programmed with the current vehicle configuration information. For additional information on module programming,
Refer to: Module Configuration - System Operation and Component Description (418-01A Module Configuration, Description and Operation).
When an ABS or stability control fault has been corrected or a new component has been installed, the ABS module must be calibrated. The ABS Calibration procedure is required for the stability control sensors to learn the zero-position of the vehicle which means the vehicle must be on a level surface and not moving. The ABS Calibration procedure is carried out using a diagnostic scan tool.
All Wheel Drive (AWD) Mode Select Switch (MSS)
The AWD MSS is a multi-position, rotating switch and is part of the ATCM .
Brake Booster Vacuum Sensor
On vacuum brake boosted vehicles, the brake booster vacuum sensor is a piezoelectric device used by the ABS module to monitor the vacuum in the brake booster on vehicles equipped with a vacuum brake booster. The sensor is hardwired to the ABS module by 3 circuits. One circuit is for the 5 volt sensor supply, one circuit is for sensor ground and one circuit is for sensor output. The sensor output ranges from 0.3 volt to 4.7 volts, depending on the amount of vacuum in the booster.
Electric Brake Booster (EBB) Unit
Except for the brake fluid reservoir, the EBB unit is serviced as a single assembly and must NOT be disassembled.
The EBB unit contains the ABS module, solenoid valves, pressure sensor and hydraulic pump motor; the EBB unit also takes the place of the brake master cylinder, the vacuum booster, the HCU and the brake pedal switch.
When a new EBB assembly is installed, the ABS module must be programmed with the current vehicle configuration information. For additional information on module programming,
Refer to: Module Configuration - System Operation and Component Description (418-01A Module Configuration, Description and Operation).
When an ABS or stability control fault has been corrected or a new component has been installed, the ABS module must be calibrated using the ABS Calibration routine found in the diagnostic scan tool. ABS Calibration is required for the stability control sensors to learn the zero-position of the vehicle which means the vehicle must be on a level surface and not moving.
Hill Descent Control Switch
The hill descent control switch is a single-pole, momentary-contact switch and is part of the ATCM .
Hydraulic Control Unit (HCU)
Vehicles equipped with a vacuum brake booster are also equipped with an HCU .
The HCU contains the solenoid valves, the hydraulic pump motor and the pressure sensor used by the ABS for the ABS and stability control systems. While the ABS module can be serviced separately from the HCU , a new HCU comes with a new ABS module.
Stability Control Sensors
The stability control sensors for the traction control and stability control functions consist of the yaw rate sensor, lateral accelerometer, longitudinal accelerometer and roll rate sensor. The sensors are housed in the RCM which sends sensor information to the ABS module over the HS-CAN2 . If any of the sensors are defective, a new RCM must be installed.
- The yaw rate sensor measures the yaw angle which is the difference between the direction the vehicle is pointing when cornering and the direction the vehicle is actually moving.
- The longitudinal accelerometer measures the acceleration and deceleration of the vehicle as it moves forward and backward.
- The lateral accelerometer measures the force created when a vehicle corners that tends to push a vehicle sideways.
- The roll rate sensor measures the rate of rotation of the vehicle along the centerline of the vehicle from front to back.
Trail Control Switch
The trail control switch is a single-pole, momentary-contact switch and is part of the ATCM .
Wheel Speed Sensors
All 4 wheel speed sensors are active (magneto resistive) sensors that operate on the Hall-effect principle to generate a square wave signal proportional to the rotational speed of the wheel. Because these are active sensors, receiving voltage from the ABS module and sending a varying voltage back to the ABS module, they are able to detect much lower rotational speeds than passive (magnetic inductive) sensors. Each wheel speed sensor is connected to the ABS module by 2 circuits. One circuit provides voltage for sensor operation and the other circuit provides sensor input to the ABS module.
The front wheel speed sensors are mounted on the front wheel hub and are serviced separately.
The rear wheel speed sensors are mounted on the axle flange at the brake dust shield and can be serviced separately.
Wheel Speed Sensor Encoders
The wheel speed sensor encoders are magnetized, toothed rings used to create a Hall-effect switch when combined with the wheel speed sensor. The front wheel speed sensor encoders are integrated into the wheel bearing and hub assembly and are serviced with the assembly. The rear wheel speed sensor encoders are pressed onto the axle shaft and are serviced with the axle shaft.
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