P0496 - EVAP System

[KillerPenz]

Has anyone had this code yet? If so, what was your fix? I'm looking at replacing the purge valve first. Plan on testing it with a multimeter tomorrow, but figured I'd ask if anyone has had this issue. Truck was at 95,957 when the check engine light popped on.

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[Ducati1098]

Testing it with a multimeter probably wont show anything. If it is the purge valve it's likely stuck open slightly. There's a bunch of different things that can cause a small evap leak, so without diagnosis it's just a guessing game.

 

[KillerPenz]

Testing it with a multimeter probably wont show anything. If it is the purge valve it's likely stuck open slightly. There's a bunch of different things that can cause a small evap leak, so without diagnosis it's just a guessing game.

Unfortunately, that's where I am at is the guessing game phase.

Would you suggest pulling the hose and testing for vacuum as a starting point? I'd like to do something before having to bring it to a dealer for them to have it for a whole day to figure out what's wrong with it.

 

[KillerPenz]

I'm going to guess and say it's located back here near the firewall?

 

[Ducati1098]

I'm going to guess and say it's located back here near the firewall?

Yeah that's it. Take it off, and try and blow though it. You shouldn't be able to if it's closed like it should be with no power.

 

[KillerPenz]

Yeah that's it. Take it off, and try and blow though it. You shouldn't be able to if it's closed like it should be with no power.

Thank you, I'll try that out later after work.

Last question, how do you get those stupid green clips off without snapping them? Any time I've dealt with some sort of clip on or around a Ford engine, I always end up snapping them.

 

[Ducati1098]

Thank you, I'll try that out later after work.

Last question, how do you get those stupid green clips off without snapping them? Any time I've dealt with some sort of clip on or around a Ford engine, I always end up snapping them.

Just take your fingers and gently pull up and out on the ends of the green clips. They should pop off very easily

 

[KillerPenz]

Yeah that's it. Take it off, and try and blow though it. You shouldn't be able to if it's closed like it should be with no power.

Well, turns out I can't blow through it. Guess that means valve is still good?

Any thoughts on what to check next? Or am I looking at a trip to the dealer?

Or do I start the engine let it run for a few minutes and see if it opens?

 

[KillerPenz]

I will add that I got the multimeter to hit one of the prongs, other cable to metal, and it jumped to 47 ohms. not sure if it can work that way being that I can't hit both terminals, but it's what I can get to.

 

[KillerPenz]

Last bit of info, not sure if it helps at all. Ran ForScan:

- DTC Present at Time of Request
- Malfunction Indicator Lamp is On for this DTC
- Test not complete

Module: Powertrain Control Module

Freeze Frame #1:

Freeze Frame #2:
-EVENT_TIME: 124647971 s (Thu Oct 02 18:22:38 2025) - Event time
-TOTAL_DISTANCE: 95957 miles - Total Distance
-FUELSYS: Closed Loop - Fuel System Status (Open/Closed Loop)
-LOAD: 38.04 % - Calculated Load Value
-ECT: 203 °F - Engine coolant temperature
-ECT: 203 °F - Engine coolant temperature
-SHRTFT1: -3.13 % - Short term fuel trim 1
-LONGFT1: 3.13 % - Long term fuel trim 1
-SHRTFT2: -2.34 % - Short term fuel trim 2
-LONGFT2: 6.25 % - Long term fuel trim 2
-MAP: 15.1 psi - Manifold absolute pressure sensor
-RPM: 2409 1/min - Engine Revolutions Per Minute
-VSS: 78.9 mph - Vehicle Speed
-VSS: 78.9 mph - Vehicle Speed
-SPARKADV: 18.00 ° - Spark Advance
-IAT: 75 °F - Intake Air Temperature
-RUNTM: 1400 s - Time Since Engine Start
-RUNTM: 1400 s - Engine Run Time
-FRP: 2204.6 psi - Fuel Rail Pressure
-EVAP_PCT: 0.00 % - Commanded Evaporative Purge
-FLI: 41.96 % - Fuel Level
-BARO: 14.8 psi - Barometric pressure
-BARO: 14.8 psi - Barometric pressure
-VPWR: 14.43 V - Control Module Voltage
-VPWR: 14.43 V - Control Module Voltage
-TP_REL: 27.06 % - Relative Throttle Position
-TAC_PCT: 0.39 % - Commanded Throttle Actuator Control

 

[KillerPenz]

Let's just add a little bit of insight from Gemini:

Based on your ForScan results, the P0496 code on your Ford Bronco is for an "Evaporative Emission System High Purge Flow." The data you provided strongly suggests the most likely cause is a faulty canister purge valve that is stuck open.


The P0496 code means the engine's computer detected vacuum and vapor flow from the canister at a time when it commanded the purge valve to be closed. This un-commanded flow of air and fuel vapor creates a vacuum leak into your engine.



## How Your ForScan Data Confirms the Diagnosis


Your freeze frame data provides two key pieces of evidence that point directly to a stuck-open purge valve.

1. The Smoking Gun : The most important value in your data is EVAP_PCT: 0.00 %. This shows that at the exact moment the fault was recorded, the Powertrain Control Module (PCM) was commanding the purge valve to be 0% open—in other words, completely closed. Since the system still detected flow (triggering the code), it means the valve is mechanically stuck open and isn't listening to the computer's "close" command.
2. Supporting Evidence : Your long-term fuel trims (LONGFT1: 3.13 % and LONGFT2: 6.25 %) are both positive. This means the computer has been adding extra fuel over time to compensate for a lean condition (too much air). A stuck-open purge valve allows unmetered air and vapor into the engine, creating just this kind of lean condition.

The rest of the data (RPM: 2409, VSS: 78.9 mph) simply tells us the fault occurred while you were cruising at highway speed, which is a typical condition for the EVAP system monitor to run its self-test.


Keep in mind though, when I do the blow test on a cold purge valve (disconnected), it is closed.

 

[Ducati1098]

Well, turns out I can't blow through it. Guess that means valve is still good?

Any thoughts on what to check next? Or am I looking at a trip to the dealer?

Or do I start the engine let it run for a few minutes and see if it opens?

I would just bring it to your dealer. Without the right equipment you aren't
going to be able to diagnose an evap leak.

I will add that I got the multimeter to hit one of the prongs, other cable to metal, and it jumped to 47 ohms. not sure if it can work that way being that I can't hit both terminals, but it's what I can get to.

No idea which pins you are measuring or anything else, so this really isn't data you can use.

Let's just add a little bit of insight from Gemini:

Based on your ForScan results, the P0496 code on your Ford Bronco is for an "Evaporative Emission System High Purge Flow." The data you provided strongly suggests the most likely cause is a faulty canister purge valve that is stuck open.


The P0496 code means the engine's computer detected vacuum and vapor flow from the canister at a time when it commanded the purge valve to be closed. This un-commanded flow of air and fuel vapor creates a vacuum leak into your engine.



## How Your ForScan Data Confirms the Diagnosis


Your freeze frame data provides two key pieces of evidence that point directly to a stuck-open purge valve.

1. The Smoking Gun : The most important value in your data is EVAP_PCT: 0.00 %. This shows that at the exact moment the fault was recorded, the Powertrain Control Module (PCM) was commanding the purge valve to be 0% open—in other words, completely closed. Since the system still detected flow (triggering the code), it means the valve is mechanically stuck open and isn't listening to the computer's "close" command.
2. Supporting Evidence : Your long-term fuel trims (LONGFT1: 3.13 % and LONGFT2: 6.25 %) are both positive. This means the computer has been adding extra fuel over time to compensate for a lean condition (too much air). A stuck-open purge valve allows unmetered air and vapor into the engine, creating just this kind of lean condition.

The rest of the data (RPM: 2409, VSS: 78.9 mph) simply tells us the fault occurred while you were cruising at highway speed, which is a typical condition for the EVAP system monitor to run its self-test.


Keep in mind though, when I do the blow test on a cold purge valve (disconnected), it is closed.

It more than likely is a stuck open purge valve, it could be intermittently stuck open. But once again without a scan tool and the vehicle to watch live data and FTP, it's hard to say for sure.

 

[Brian_B]

This may be a dumb question, but looking at the data from Forscan and all -- since you pulled everything out have you tried just clearing the code and seeing if it returns after it's been cleared? Or are you just looking at the stored data from a previous event that won't clear until you hit reset?

Also, I've broken some of those clips - you can ziptie around if the clip breaks to hold the hose in, as the clip just holds the harness in and snug. If you break the harness though - screwed.

Now sure what the ECM is using to detect flow through the canister - the canister itself is up by the fuel tank under the passenger side. Could be as simple as a loose hose, and by pulling the valve you just fidgeted with 3/4 of all the connections right there.

 

[Ducati1098]

Now sure what the ECM is using to detect flow through the canister - the canister itself is up by the fuel tank under the passenger side. Could be as simple as a loose hose, and by pulling the valve you just fidgeted with 3/4 of all the connections right there.

It monitors fuel tank pressure

 

[Brian_B]

FRP: 2204.6 psi - Fuel Rail Pressure

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