3.91 Gear Change, Limp Mode HELP!!!!

[vjo90rs8]

Hi DS,

Just had my 3.91 Getrag gears/differential installed on my 2012 Dodge Charger R/T Road and Track and the car is going into limp mode. I have set the gear ratio to 3.90 and the speedometer is correct but I get a "Forward Collision Warning/Adaptive Cruise Control" DISABLED alert "Service Sensor" at startup, then right after starting the drive it goes into limp mode. If I restore back to default the ALERT goes away. I tried pulling the fuse but it did not help.
When in limp mode I get a U0104 code: communication to FCW/ACC lost, that is the reason it is going into limp mode.
I think I need a custom tune sent to delete this code or delete the limp mode and / or ACC/FCW.

I will be calling first thing in the morning.

I NEED HELP ASAP!!!!

[mikel]

update your tool

[vjo90rs8]

Updated to "I" with Garrett's help, did not solve the issue.
Also tried disconnecting the battery, no help.
right when I program the gear ratio with the Trinity the FCW/ACC disable warning turns on.
When I put the car into the ON position or start the car the warning alert comes on and the car goes into limp mode at 1-2 shift.

If I unmarry the Trinity (stock setting of 3.06) the FCW/ACC alert does not come on at startup but the car still goes into limp mode at the 1-2 shift (and FCW/ACC alert warning comes on, makes sense since the car is in limp mode). I drove the car around the corner with the 3.06 setting in limp mode and the speedo seems to be correct (maybe because the speedometer reading comes from the wheel sensors and not the rotation of the driveshaft). Since the 3.06 and 3.91 gear ratio setting show the same behavior (with except of the instant FCW/ACC warning) tt is almost as if the car never actually takes the 3.91 get setting from the Trinity.

[vjo90rs8]

I'm calling back again. I would hate to have to get the stock rear put back on.

[mikel]

Well, we're not sure whats causing the FCW issues, or why the car is limping with the gears adjusted.

It seems the ABS is not happy about the gear ratio you are selecting, which is why the FCW is not liking it.

The most immediate resolution I have would be to have you send us the TCM, and we could program the 3.91 ratio in the TCM itself.

[vjo90rs8]

I'll remove it and overnight it today. What is the address? The one in the contact section?
Also, can you overnight it so that it will be here at least by Friday.

Thank you,
David Oraboni

[email protected]

[vjo90rs8]

New TCM seems to have fixed the issues!!!

One more question, I should be able to plug in the Trinity and program shift firmness through the "quick adjust" menu without issues right?

Thank you for all your help!!!

[mikel]

Yes, you can make any changes, just leave the gear setting alone

[vjo90rs8]

Thanks! Yes, gear setting is not going to be touched!!!!

[BdyGrd]

Nice!!! I bet that new gear is a blast!
Sounds like DS gave ya some awesome support on this!!!
If so, please give them mad love on here!! All you ever see is negative posts, over & over again!
(I am in no way affiliated with them.)

[mraisi]

This is really nice to hear!

mmm where did u get the new gears from and how much ?

[vjo90rs8]

I got the parts from Steve White Parts.
The following parts cost about $1400.
3.91 Getrag, axles, 392 coupler, pinion bolt / mounts, coupler bolts / nuts, axle nut, and fluid.

[Strieg3]

Just did this same rear end change on my '11 Charger R/T, man what a difference! Thanks to the info in this thread the job went smooth with no issues, knew exactly what to do with my Trinity so thanks for posting up the info.