FORScan forum

We receive many complaints that on new cars (usually after 2011-2013 model years) changing tire size in BdyCM causes P1635 in PCM and/or TCM.

Models app. after 2011-2013 model years keep tire size and axle ratio in BdyCM and other modules (first of all, PCM and TCM) load it from there. Some models have no dedicated TCM module. In these models PCM manages both engine and transmission.

PCM usually requires special function to learn related changes in BdyCM module. This function in FORScan is called "Configuration and Programming->PCM module initialization/relearn vehicle data". As for TCM, only some of them have this function actually implemented. FORScan has no ablity to determine if the TCM has the learning function supported or not. So it shows this function in the list for all TCMs. If you get error in this function, it most likely means that this function is not really suported AND is not necessary because TCM learns new tire size in an automated mode.

So far our investigations and investigations of our users show the following:

1. if tire size is changed AND PCM and/or TCM have not learnt the new tire size, the P160A code will most likely appear. In this case owner needs to run PCM and/or TCM module initialization/relearn vehicle data function.

2. If P1635 appears in PCM or TCM after tire size change, it means that the module has learnt the new tire size, but this tire size is out of allowed range . Actually, this is exactly what P1635 DTC description tells us about:

P1635 - Tire/Axle Out of Acceptable Range

We suggest a simple test to check this. PCM and TCM modules usually have a TIRESIZE (or similar) PID that shows tire size in revs/mile or revs/km (depends on FORScan settings). Owner can add this PID to the Dashboard and check after the tire size change in BdyCM configuration (learn function may be necessary). The BdyCM parameter is the tire length (2 * Pi * R * 0.967) and TIRESIZE parameter is in revs/mile, but these parameters can be easily converted from length to revs/mile or vice versa.

At this moment the tests show the following behaviour:

i. If the new tire size is in acceptable range, the TIRESIZE is changed and matches (learn function may be neccessary)
ii. if the new tire size is out of acceptable range, the TIRESIZE becomes the lowest (or highest) possible value.

We suspect the tiresize limits are hardcoded in TCM firmware. The transmission as built data (TRID block) usually contain transmission strategy and solenoid ID numbers and doesn't seem to have the limits (but we cannot guarantee it). Also we do not recommend to play with TRID block as transmission strategy and solenoid ID are critically important for normal transmission work and if these values are incorrectly changed, it will be not good for the transmission health at all.

Update 2019-11-08: It seems MY2018+ models throw U0422 "Invalid Data Received From Body Control Module" instead of P1635. Also for new models it seems to be not possible to read "actual maximum allowed" tire size.

Hello I changed my rear axle ratio in a 2017 Mustang Gt PP from 3:73 to 3:55 in the BCM. I am getting a U0422-2F DTC instead of the DTC you are mentioning. When I run the PCM relearn procedure it doesn’t resolve the DTC. When I set the ratio back the DTC resolves.
Is it just that I can not start the PCM relearn properly or is this a different issue?

Hla86 wrote: Tue May 08, 2018 3:30 pm Hello I changed my rear axle ratio in a 2017 Mustang Gt PP from 3:73 to 3:55 in the BCM. I am getting a U0422-2F DTC instead of the DTC you are mentioning. When I run the PCM relearn procedure it doesn’t resolve the DTC. When I set the ratio back the DTC resolves.
Is it just that I can not start the PCM relearn properly or is this a different issue?

Pcm relearn function on mustang 2015 and early not working. I am 100% sure. I try many times. With IDS no problem.

Dear all,
I tuned AT/BF Goodrick Tires 265/75/R18 for my Ranger
I changed in BdyCM 726-12-01 xxxx 09AB xxxx with Forscan
But appeared Check engine indicator and DTC P0700 in PCM, and I cannot reset or relearn PCM.
What can I do? Thanks

Posted this in the beta forum as well.

2018 Expedition.

Get PCM and TCM P160A.

Cannot relearn PCM.

when doing anything like this on cars after 2015 , write BCM module then on same window should have write to other secoundary module , do that as well ( should write same to ipc ), then turn ignition off for 30 secounds , then turn on and use relearn on pcm if required , but leaving ignition off should make it relearn when turning ignition on.

I have a 2018 F350 that I have installed 38x13.50-20 tires and tried using the google doc spreadsheet to modify BCM line 726-12-01 with the value that was calculated by the algorithm given at the link below

https://docs.google.com/spreadsheets/d/ ... U/htmlview#

After I modified that line I clicked write and then cycled the truck on and off before returning to the programming screen to run the PCM module initialization/relearn vehicle data function.

After all of that I get the Check Engine Light in the dash and the DTC code is P1635. I tried running the TCM module initialization/relearn but every time it says the operation was interrupted and it doesn’t work. I cannot get the value I changed on BCM 726-12-01 to work so I changed it back to the original value.

If anyone can please help it would be greatly appreciated because my truck shifts sluggish and the speedo is way off.

I had previously set my tire size to a 35" size (BCM 726-12-01 set to xxxx-0AAB, if memory serves) and my axle to 3.31, which correctly set the speedometer for my 3.55 with 37x13.5 tires. I got the 160 error which, I have read, is fixable with the PCM relearn.

I read on Ford-trucks.com that someone had successfully set their BCM to the 37" tire size with the latest FORScan so I tried putting my axle back to 3.31 and set the BCM to xxxx-0AEE. Now I have the P-1635 error. I have driven the truck to see if the shifting is any different than before.

Do I need to flash to the stock tune before I perform the relearn to resolve p160A? 2015 SHO changed tire size from 20 to 18 inch

Do I need to flash to the stock tune before I perform the relearn to resolve p160A? 2015 SHO changed tire size from 20 to 18 inch