How to: Recalibrate Speedometer with Forscan for 2021 Bronco

[ClappinCheex369]

Yes it’s very much a trial and error it seems. Went to the 285/75/17 for my winter tire package and seems like 2567 got me bang on. Always found the 2653 was off by a mph showing higher than actual right from stock so this fixed change and I’ll wait to see how it is once I put the Sasquatch tires back on in spring.

How is the speedo with the stock sas wheel/tires back on with that number?

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[ClappinCheex369]

Is this still accurate/the way to change tire size with 2.3.70?
just downloaded forscan

Use the PCM service function instead of the PCM relearn. The PCM relearn doesn't work.

UPDATE: on new Forscan versions (2.3.52+), " PCM Module initialization/relearn vehicle data" is reported to work.

Detail:
1- I used FORScanSetup2.3.47.test20220221 (version that supports MY2022 goat modes) with OBDLink EX. You will also need a FORScan demo license.
FORScanSetup2.3.47.test20220221.exe

2- Set front/rear TPMS and tire size in BdyCM. For KM3 37x12.50R17D on sasquatch wheels, use 35psi and 2760mm. For sasquatch stock tires and wheels, use 39psi and 2653mm. Tire circumference cannot exceed 2800mm. DTC's will be set in 2-3 modules that will need to be fixed.

3 - To fix the non-PCM DTC's, run the AWD relearn. Don't run the PCM relearn (it doesn't work).

4 - Clear the DTC's. All should be cleared except PCM.
5 - Run the PCM reset-all-adaptations service function. This will fix the size mismatch and also clear the PCM DTC. It will relearn the engine/trans/fuel adaptations over time while driving. UPDATE: on new Forscan versions (2.3.52+), " PCM Module initialization/relearn vehicle data" is reported to work.

6 - Confirm all DTCs are cleared.

7 - Install a free speedometer app with tenth-mph readout on your phone and testdrive to confirm speed is within 0.5mph at 60mph cruise control. For new tires, the actual speed should be a little higher than speedo. For worn tires the actual speed will be a little less.

 

[Brian_B]

Is this still accurate/the way to change tire size with 2.3.70?
just downloaded forscan

Yup.

If the DTC codes won't clear - verify you have a valid number in for the tire size and redo the PCM and AWD Reinitialization routines.

 

[HPNQ420]

Yes it’s very much a trial and error it seems. Went to the 285/75/17 for my winter tire package and seems like 2567 got me bang on. Always found the 2653 was off by a mph showing higher than actual right from stock so this fixed change and I’ll wait to see how it is once I put the Sasquatch tires back on in spring.

If the digital speedometer is consistently showing 1 mph high it is likely correct and programmed to read 1 mph high. If the calibration is off this deviation will increase with speed. Once I had mine dialed in it read 1 mph high from 20 mph to 90 mph

 

[TeocaliMG]

I posted to this thread like 3 years ago back when I went to 37's, went through the typical troubleshooting of finding the right tire size and getting the right module reset (had an older version of forscan then too).

Fast forward to now, I finally got regeared (from 4.7's to 5.38's) after 3 years of sparsely using 6th gear (manual). I got the speedo well matched, wrote 5.38 and 2760 in the BCM and that's just about dead on for me. But it seems that no matter what I do with module resets I cannot get cruise control in 5th or 6th gear, and even in 4th gear its temperamental (not sure if the limitation is speed or overdrive or something else).

Reluctantly posting here for help because I am frustrated that I cannot figure this out, after having essentially figured it out (tire size only) 3 years ago.

Saw a similar post here by Eric, explicitly including gear change, in case there is something unique with that beyond the more typical tire size change we see in this thread.

I changed my tire size about 1.5 years ago when I put 37s on and didn't have any errors. I just changed my axle ratio to 4.88 (had Dana 60 installed a while ago) and changed my tire size back to 2800 and still getting errors

If it is possible to screw the pooch on the ABS, I may have done that, while snooping into modules I noticed that the ABS also had a gear selection and tire size, though it was multiple choice, not writable like the BCM. Perhaps it's irrelevant but I tried changing those values and the ABS threw a fit, said it couldn't do that combo, and now whenever I open the ABS those options are straight up gone... Not sure why, but I lean towards thinking that was irrelevant and all I need to do is write the new values in the BCM, then relearn/reset for sure: PCM/AWD and perhaps optional: ABS/TCM (manual).

Anyway, if someone has changed gears on their bronco and knows exactly which modules need to be reset, and if there is a particular order that must be followed, or drive cycles between different module resets, please let me know!

 

[Badassbronco]

I changed my values to 2653 to 2760.
Relearned Awd and PCM. Went to. Learn DTC and I get errors and says unable to read DTC.

At first I had all the errors after I changed tire size such as 4x4.
I started Bronco and drove it and I only see an engine light flash before I start the car now

 

[Badassbronco]

If anyone cares I got it back to stock today. I decided to try driving it a few days to get some "drive cycles" on it then try rerunning the bcm an put the stock tire size in. did a reset to the pcm awd an all the lights cleared an it was back to normal with the speedometer off.

Tomorrow I'll try to write the corrected tire size, run awd relearn, clear dtc codes an a pcm reset. I think that's the process from reading all this multiple times!

Did you ever retry and get the speedo recalibrated?

 

[Langwilliams]

Did you ever retry and get the speedo recalibrated?

I did. I forgot what I was doing wrong but I did finally get it.

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