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

**Joe_** · 04-07-2021, 08:33 PM

Hello everyone, I wish my first post had been under better circumstances but I have a major problem.

After a lot of trouble I managed to get a Getrag rear end with 3.92 installed in my car.
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** · 04-07-2021, 10:09 PM

Did you change axles?

**Joe_** · 04-07-2021, 10:19 PM

Originally Posted by Hemihackman

Did you change axles?

Yes I changed the half shafts along with the center differential, 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.

**Hemissary** · 04-07-2021, 11:31 PM

Are you sure the diff is indeed equipped with 3.91 gears?

**Joe_** · 04-08-2021, 12:26 AM

Originally Posted by Hemissary

Are you sure the diff is indeed equipped with 3.91 gears?

Yes I had the mechanic count the gears himself and also check the driveshaft rotation compared to the tire rotation he assured me that of 3.06/3.71/3.92 it was a 3.92.

**Hemihackman** · 04-08-2021, 07:29 AM

Can you give me a part number on Getrag -the label.

**CruzKing** · 04-08-2021, 08:43 AM

had a simular problem when i put a getrag in my RT, the mechanic forgot the tone rings.could be bad or missing.

**Joe_** · 04-08-2021, 09:12 PM

Originally Posted by Hemihackman

Can you give me a part number on Getrag -the label.

Yes, it is part# 05038237AE
and it says 3.91 on the label.

**Joe_** · 04-08-2021, 09:13 PM

Originally Posted by CruzKing

had a simular problem when i put a getrag in my RT, the mechanic forgot the tone rings.could be bad or missing.

But if that was the case wouldnt there be a traction control light or check engine light with an error code? All my lights are off and traction control seems to be happy, no issues.