Anyone deal with U4128, Limp Mode while going down hill?

[Avar928]

2018 JLUS 2.0 with 105,000mi currently on a road trip across the US and my Jeep has been throwing U4128 and going into limp mode on certain downhill sections lately. I get the Service Electronic Stability Control message as well. Normally if I pull off and shutdown and restart it'll go away and drive normally. Doesn't happen on all downhills, noticed it first when I hit western CO going into UT on a curvy downhill mountain section. Google searches show up different suggestions but it's a communication network issue for a torque reading apparently.

Check battery?
Main battery pre-start voltage is 12.8 and while running is 14.0 getting charged, about 2yrs old. I have the BSG e-torque so no AUX battery aside the 48V under the passenger rear.

Steering misalignment?
Tracks straight relative to what I consider normal.

No other related symptoms. Anyone else seen this and know what to check? I have to haul back home this week about 1,000mi. I have a Pulsar XT but haven't read anything about it going whack and causing problems.

SOLVED thanks to Rhinebeck01 —-
It was the Pulsar XT, removed and no replication under same conditions. Seems like the Pulsar started to bug out down hill (on public road at whatever posted speed of traffic). May happen to any throttle controller device or device with such function added on.

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[Rhinebeck01]

2018 JLUS 2.0 with 105,000mi currently on a road trip across the US and my Jeep has been throwing U4128 and going into limp mode on certain downhill sections lately. I get the Service Electronic Stability Control message as well. Normally if I pull off and shutdown and restart it'll go away and drive normally. Doesn't happen on all downhills, noticed it first when I hit western CO going into UT on a curvy downhill mountain section. Google searches show up different suggestions but it's a communication network issue for a torque reading apparently.

Check battery?
Main battery pre-start voltage is 12.8 and while running is 14.0 getting charged, about 2yrs old. I have the BSG e-torque so no AUX battery aside the 48V under the passenger rear.

Steering misalignment?
Tracks straight relative to what I consider normal.

No other related symptoms. Anyone else seen this and know what to check? I have to haul back home this week about 1,000mi. I have a Pulsar XT but haven't read anything about it going whack and causing problems.

@Avar928

Undoubtedly, the culprit is your Pulsar XT. It's causing the JL to go into limp mode by improperly doing throttle control.

Regardless of the throttle controller they can throw the JL into limp mode if throttle control changes/settings are made while you are actively working the gas pedal.

You might want to remove the Pulsar XT til you get home. Test/drive without it in the mix for awhile and see if the problem subsides... then you will know..

Unless you want to be dealing with clearing code so you can get out of limp mode..

How long have you had the Pulsar XT?

 

[Avar928]

I've had it for at least 2yrs if not 3, I did the same trip last year with it no problem. I'm possibly thinking it may be going bad. I'm going to remove it and make a short trip to a section where I know I throw the code and see how she behaves.

 

[Rhinebeck01]

I've had it for at least 2yrs if not 3, I did the same trip last year with it no problem. I'm possibly thinking it may be going bad. I'm going to remove it and make a short trip to a section where I know I throw the code and see how she behaves.

@Avar928

Could be a buggy firmware update you did to the device... and that has it now screwing up.

Yes, remove and test without the device.

 

[Avar928]

Or no updates since it's same version out of the box. Thinking it's just bugging out and will reach out to the vendor on it if that is the case.

 

[Rhinebeck01]

Or no updates since it's same version out of the box. Thinking it's just bugging out and will reach out to the vendor on it if that is the case.

@Avar928

I had a Pedal Commander I used on my 2018 JL for about 5 years +-. Worked great ... and I knoew not to change modes while working the gas pedal...

Then after all those years the chitt hit the fan. For no reason the thing was causing Limp mode, codes and such. I had to remove the Pedal Commander for good..

 

[Avar928]

Yep, looks like it was the Pulsar XT going bad on me. Drove around took the same path I threw codes and she’s just fine. Definitely don’t plan on reinstalling it, and while I do miss the extra bit of butt dyno boost I’d rather have an error free vehicle.

Thanks!! Problem solved. Now to trace this turbo coolant leak…

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