2006 Dodge Magnum R/T - Getrag swap - Limp mode problem

[Joe_]

Hello everyone, I have a major problem and any help would be greatly appreciated. I figured out this problem could probably apply to 2006 Dodge Charger R/T as well as my 2006 Dodge Magnum R/T so am posting it here.

After a lot of trouble I managed to get a Getrag rear end with 3.92 installed in my Magnum.
My Predator2 has different options for rear end ratios and I figured that there shouldn't be an issue as I would just program the 3.92 ratio and simple...

This is what is happening now:
Ever since the swap when I drive the car it stays in Limp mode 2nd gear, autostick does not work. Every time I drive the car I get the P0731 code which is first gear ratio wrong.

I then realized that doing this for 3 key cycles had caused the Limp mode to become permanent in the TCM so I took it to a Chrysler dealership and had them clear the TCM error code. Once this was done and they confirmed it was cleared I took the car for a drive and it was still in limp mode. So I retuned it again with the predator2 and again had 3.92 in there just to be safe to make sure that the code would go over into the TCM. Well that didn't help and it was still in limp mode, but each time I would drive the car I would make sure to clear the P0731 code so that it would not see the code 3 key cycles in a row and put it again permanently into the TCM.

The car has no other error codes, the traction control and wheel speed sensors seem to all work fine.

Now that I don't have the limp mode code stuck in the TCM when I start the car I can actually shift the autostick and the car appears like it will shift but after driving for 30 feet or more it again goes into limp mode immediately and the autostick gets stuck on whatever number I had it and then upon shutting off the car and turning it on again I get the P0731 code.

Before I got the rear end installed the transmission was working just fine and the shop confirmed they did not touch anything that had to do with the transmission.

The Dealership looked into the TCM with their WiTech scanner and confirmed that there are no error codes saved into the TCM at this time and they even looked up changing the rear ratio themselves and saw that they had no option to change the ratio but that the TCM in my car said in their computer "TCM (SRT)" indicating that it must be configured as an "SRT" or have accepted the 3.92 ratio from the PCM.

I am at wits end and this has all gone on over the last 3 weeks. I was wondering if there is a problem with the 2006 R/T specifically in maybe the way traction control or abs is set up so that even though the PCM and apparently the TCM think the rear should be 3.92 there is some third step in the process that is not working with the 3.92 gear?

Any suggestions would be greatly appreciated. Sorry for the long post.

By the way I am in Toronto and if anyone knows of any specialists that could sort this out in or around Toronto it would be very helpful.

[Hemihackman]

Did you change the axles?

[coanan]

What did you use to program the 3.92 gear to car?

[Joe_]

Did you change the axles?

Yes I changed the half shafts along with the center, as the stock ones are different. I got the whole thing out of a crashed 2010 Dodge Challenger R/T 6 speed manual, so I had all of the parts to swap over.

[Joe_]

What did you use to program the 3.92 gear to car?

I used my Diablosport Predator2 which has a variety of differential ratios you can pick when putting in the canned tune they provide.

[coanan]

I used my Diablosport Predator2 which has a variety of differential ratios you can pick when putting in the canned tune they provide.

Ya. that should have done the job. Did you try uninstall to factory and reinstall?

[Joe_]

Ya. that should have done the job. Did you try uninstall to factory and reinstall?

I had tried that initially a few weeks ago when I picked up the car from the shop after the rear end install, but haven't re-tried that in the last week after having the TCM cleared. Do you think flashing back to stock without moving the car and then re-uploading a tune again without moving the car around (so that there are no codes thrown) may work? I guess it is worth a shot.

I'll give it a try and post how it goes.

What I have done a few times is make minor changes to the tune with the 3.92 ratio still selected and then re-uploaded it. The minor change would be nothing important like changing raised value speed limiter back to stock speed limiter value for example.

[BryGuy]

Are you 100% sure of the ratio? Contact Authentic Performance in Scarborough. They’ll get you figured out.

[Hemihackman]

Do you have picture of label on Getrag?

[Joe_]

Are you 100% sure of the ratio? Contact Authentic Performance in Scarborough. They’ll get you figured out.

Thank you very much for the suggestion, will check them out.
Yes I'm sure about the ratio, the diff has 3.91 on the label with the bar codes

[Joe_]

Do you have picture of label on Getrag?

Hi I got a picture of it but I am not sure how to put it on here so I can tell you wat it said..
It says GETRAG on the top and there are two bar codes. The bottom bar code has part# 05038237AE on it and then further on the right it says 3.91

[Joe_]

Ya. that should have done the job. Did you try uninstall to factory and reinstall?

Yes as per your suggestion, today I put it back fully to stock and then tried to input the tune again with 3.92 gear selected but still same problem.
Trans almost immediately upon starting to drive goes into Limp mode and stopping and parking the car leads to a P0731 Code popping up. It is the only code, there are no other codes and until P0731 pops up there are no trouble lights on the dashboard. No issues with traction control or anything.

This makes me wonder if there is the possibility there is an error stored in the FCM. I had the TCM cleared at a dealership but I had not asked them about the FCM, I don't even know if it can store codes.

[funkpolice]

I would guess is a tone ring issue.

[Joe_]

I would guess is a tone ring issue.

Since the tone rings are also needed for the ABS wouldn't there be other lights like wouldn't the traction control and ABS lights be on?
My instrument cluster has no lights on indicating any abs/traction problems.

[funkpolice]

yeah, probably. I messed up a tone ring when I changed my axles, but it was a long time ago. I don't remember if the dash lit up or not.