How to: Recalibrate Speedometer with Forscan for 2021 Bronco

[adrewpower]

Thanks for the responses! If I clear the logs, rerun the read DTC, and don’t come up with any errors then I should be ok?

Did you get this all cleared. I’m curious before I go down this path again. The first time with the previous software version, it gave me the 160A error which caused me to panic and run to the dealer to get it put back to the way it was. Hopefully it now all works and all DTC errors and PCM codes are corrected. Really want the speed to be correct but more so I want my miles to be accurate. Let me know if you don’t mind.

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[pborrica]

Yup!

Thanks for confirming!

Did you get this all cleared. I’m curious before I go down this path again. The first time with the previous software version, it gave me the 160A error which caused me to panic and run to the dealer to get it put back to the way it was. Hopefully it now all works and all DTC errors and PCM codes are corrected. Really want the speed to be correct but more so I want my miles to be accurate. Let me know if you don’t mind.

Yup! Was able to get it all cleared. Once I cleared the DTCs and reran the read DTC after following the posted instructions I did not come up with anymore issues

 

[adrewpower]

Thank you to everyone that’s contributed to this process.

 

[Ruggles]

So everything has been fine since doing this on mine but even when putting in the new circumference of my tires my speedometer is still off by approx 2 mph. I went from 255/70/18's to 285/70/17's. Is being 2 MPH off make much difference or can you get it exactly where it should be? Any suggestions on what increments to change the circumference to to get it closer if it is worth it?

I'm off by the same amount in my Big Bend after switching to 285/70/17's. Does anyone know if the speedo is approx 2MPH off from the factory? All my past Fords have read faster than any GPS I've used, just wondering if I should keep messing with it to get it closer or if 2MPH fast is how they come from the factory anyway, because if that's the case it's close enough for me. I never checked my speed with GPS before swapping to bigger tires and I'm wishing I did!

 

[22OBX]

I'm off by the same amount in my Big Bend after switching to 285/70/17's. Does anyone know if the speedo is approx 2MPH off from the factory? All my past Fords have read faster than any GPS I've used, just wondering if I should keep messing with it to get it closer or if 2MPH fast is how they come from the factory anyway, because if that's the case it's close enough for me. I never checked my speed with GPS before swapping to bigger tires and I'm wishing I did!

Quite possible. 2558 is the circumference of a stock OBX 255/70/18 and 2475 is what Ford programmed. I went to a 275 and only off by 1 mph.

 

[GRAYFOX-SVT]

I'm off by the same amount in my Big Bend after switching to 285/70/17's. Does anyone know if the speedo is approx 2MPH off from the factory? All my past Fords have read faster than any GPS I've used, just wondering if I should keep messing with it to get it closer or if 2MPH fast is how they come from the factory anyway, because if that's the case it's close enough for me. I never checked my speed with GPS before swapping to bigger tires and I'm wishing I did!

Quite possible. 2558 is the circumference of a stock OBX 255/70/18 and 2475 is what Ford programmed. I went to a 275 and only off by 1 mph.

When I was off by 2MPH I changed the circumference by 50 each time and by the end lowered it by 100 total from where I was when I was off by 2MPH. Now it matches what Waze shows and an app I have on my phone. It still may be off by maybe a 1/2 mph so I’d only change it by a factor of 25 if I was to mess with it again. Sometimes it takes the app a second to catch up to the mph on the bronco so that’s why I think it might be off by a 1/2 mph

 

[capterik]

I have a base bronco and acquired some tires off a big bend, 255 75 17, does anyone know the circumference and tire pressures used from factory for these?

 

[capterik]

This happens on 2021+ F150's and 2020+ F250/350's as well. Not sure if it's affecting newer Mustangs yet.

FORscan is not yet able to correctly initiate the PCM relearn on the newer models for some reason. It works fine on the older ones. I know this is of no help since there isn't an older Bronco that the PCM relearn would have worked correctly on, but hopefully that provides some context to the situation. I suspect it will be resolved in the next several months with a new version of FORscan, but I don't have any inside track on FORscan development.

As posted above, the tool that the dealers use to do a PCM relearn does work, so that's an option. FORscan is free software that mimics $$$$ software/hardware the dealerships use, so that's why it's behind the curve a bit. Give it time.





While I am not going to say that Ford isn't being sloppy and getting things wrong, I can confidently say that there is a factor missing from the video in the OP and the instructions on the FORscan.org thread linked in the spreadsheet: a tire's revolutions per mile won't exactly equal the nominal diameter of a given tire size. You can confirm this for yourself by looking at specs on TireRack, which usually provides a revs per mile figure. Tires aren't rock-hard, they're inflated with air and have some give and squish to them. This is why the revs per mile figure differs from the nominal (or even actually measured) tire circumference.

Obviously, your speedometer needs calibrated to the revs per mile, not the nominal tire size.

In my calculator spreadsheet, I account for this by setting the final value to 96.7% of the calculated nominal size in millimeters. This is consistent with what Ford does for the F150, Mustang, Fusion, and a few other vehicles I've looked at. I've not poured over enough Bronco .ab files to see what they're using there. It's actually different for every tire model, but 96.7% will get you in the neighborhood. If you don't apply that correction factor, the truck will think it has a bigger tire than it really does and the speedometer will read fast.

My spreadsheet is here, you'll have to copy/paste the link to the Google Sheet since if I make the link hot, the forum will try to embed it and you won't be able to use it:

docs.google.com/spreadsheets/d/1mWnuQZlDTUGjKjmJje1QJIR8Z2c7Kf8KBZxKnw_8EqU

Make sure to follow the instructions at the top to make a copy that you can edit. You'll need to do this on a PC, it won't work on mobile.

If you want your speedometer to be dead-nuts on, there's a procedure at the bottom of the spreadsheet to do "GPS truing" as well. That's the best method if you're OCD about it. Every different model tire of a given size will have a slightly different revs per mile, which is where the variance comes from.



A word of warning about just leaving the P160A DTC in the PCM. That DTC is there for a reason and it's telling you the PCM is mad about something.

These vehicles rely on a number of sensors - four wheel speed sensors and a speed sensor in the transmission at least. Some Ford vehicles have a sensor in the diff too, not sure about the Bronco.

I can tell you from personal experience in a Mustang that after having corrected my tire size and then driving around with the P160A DTC, I experienced some drivability oddness that should give you pause. There was a dead spot at a certain RPM in a certain gear. When I hit that dead spot, I could floor the accelerator and the car would not speed up. Only way to get through it was to completely let off the accelerator for a beat and then mash it again.

Others (in the Mustang and F150 communities at least) have reported similar things. I think where it happens may be different for each tire size, because it's probably some mathematical formula that's freaking out once two values don't match by a certain amount. And that probably varies with how different your tire size is in your BCM vs what your PCM thinks it should be.

I'm not saying this could cause damage, it hasn't that I know of. But every Ford vehicle is a little different, and I'd hate to see a lean condition frying engines just because people want their speedometers reading correctly after fitting bigger tires.

These issues went away for me in my Mustang after doing the PCM relearn successfully.

how do I access these lines to make the changes, I used your spreadsheet, got what changes that it says to make for my tires, just cant seem to find this using forscan. Thanks for everything

	Set BCM line 726-15-01 to the following:
	Set BCM line 726-15-02 to the following:

 

[‘21OBX]

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

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.

I was all excited now I see I don’t have the pcm adaptation line you do. Or I don’t know where to find it.

 

[‘21OBX]

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

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.

Where did you find the pcm reset I have the latest version of forscan and don’t see it in my list.

 

[rtaylor]

Where did you find the pcm reset I have the latest version of forscan and don’t see it in my list.

Try clicking on the wrench on the left side of the screen to see the service procedures.

 

[‘21OBX]

Try clicking on the wrench on the left side of the screen to see the service procedures.

There it is thank you!

 

[Jsullivan]

Try clicking on the wrench on the left side of the screen to see the service procedures.

I reset the

There it is thank you!

I dot the P160 code, reset the awd configuration and had no other prblems. I cleared all DTC’s and was good to go.
FYI if you have a gps or phone app, compare the speeds at 60mph.
In my case speedo on Bronco said 60, hen app said 65.
Divide 65/60 =1.083. Multiple the existing circumference by 1.083 and my speedo is exact at all speeds.

 

[‘21OBX]

I reset the

I dot the P160 code, reset the awd configuration and had no other prblems. I cleared all DTC’s and was good to go.
FYI if you have a gps or phone app, compare the speeds at 60mph.
In my case speedo on Bronco said 60, hen app said 65.
Divide 65/60 =1.083. Multiple the existing circumference by 1.083 and my speedo is exact at all speeds.

For whatever reason my awd will not relearn or reset. It does in my ‘21 but the wife’s ‘22 won’t. Got the pcm code cleared tho. We set both our cruise controls at 70 she was 6mph off. When I changed the tire circumference I used two different gos apps. It’s now bang on. I’ll try again tomorrow or when we put the doors back on.

 

[Jhuff]

My Sasquatch tire circumference is listed in Forscan as being 1.2“ shorter than the advertised diameter of the tires. Does anyone know why? I guessed in another thread that Ford may account for tire wear and set the baseline as a completely bald tire?

On that note, the tires I added were .5“ taller than Sasquatch. I simply added that to what Forscan "says" I have, then computed the proper circumference. My dash reads only 3mph slower than gps. Might tinker some more for more accurate mpgs.

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