P1635 in TCM or PCM after tire size change

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FORScan
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P1635 in TCM or PCM after tire size change

Post by FORScan » Sat Apr 07, 2018 12:17 pm

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.

Hla86
Posts: 1
Joined: Wed May 02, 2018 7:08 pm
Vehicle: 2017 Mustang GT

Re: P1635 in TCM or PCM after tire size change

Post by Hla86 » 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?

stundentas
Posts: 15
Joined: Fri Oct 21, 2016 6:09 pm
Vehicle: mustang escape c-max about few years old
Location: Lithuania

Re: P1635 in TCM or PCM after tire size change

Post by stundentas » Sun Jun 24, 2018 8:16 pm

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.

tienbamboo
Posts: 2
Joined: Fri Dec 22, 2017 10:50 am
Vehicle: Ford Ranger Wildtrack 3.2 2017

Re: P1635 in TCM or PCM after tire size change

Post by tienbamboo » Tue Aug 21, 2018 10:23 am

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

benyl
Posts: 2
Joined: Thu Aug 23, 2018 12:35 pm
Vehicle: Expedition, 3.5TT, 2018

Re: P1635 in TCM or PCM after tire size change

Post by benyl » Wed Oct 03, 2018 4:38 pm

Posted this in the beta forum as well.

2018 Expedition.

Get PCM and TCM P160A.

Cannot relearn PCM.

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