U0101 / U0129 Codes and CEL

relevante · May 6, 2019

The check engine light just came on in my new GMC with just over 2k miles on it. I just towed for the first time yesterday, but not a heavy load (definitely under 3000 lbs). I pulled the codes just now and got:

U0101 Lost Communication with TCM

U0129 Lost Communication with Brake System Control Module

I'm probably going to have to take it in to the dealer, but first wanted to see if this is a common issue or if there are any relevant bulletins or recalls out first, just so I can go in well-informed.

Thanks.

tbarn · May 6, 2019

PIT5664A MAY be related .Fix is to reprogram ECM.

relevante · May 6, 2019

4 minutes ago, tbarn said:

PIT5664A MAY be related .Fix is to reprogram ECM.

Thanks. That looks like a likely candidate. Does anyone have a copy of the full document?

relevante · May 7, 2019

14 hours ago, relevante said:

Thanks. That looks like a likely candidate. Does anyone have a copy of the full document?

I just signed up for a 1 day repairprocedures.com subscription. It's $15, but they have a pretty awesome archive of info, including what appears to be a full service manual.

Anyway, the details on this seem to be that the system sees the battery voltage dropping while parked, which makes sense because I just added a BlackVue dashcam system with park mode that's drawing power while the truck is off, as long as the battery doesn't get too low. When the system sees a low voltage, it tries to wake up some other modules to do various things. But in earlier versions of the software, the codes that it sends to wake up those other modules may not be correct. There's an updated software that became available on 3/18/19. My truck was built about a week before that.

tbare54 · August 27, 2019

relevante

did they get your truck fixed from the u0101 and u0129 codes that it was showing! what was the problem if you don't mind me asking, mine throw the same codes this evening.

Bikeman · August 27, 2019

On 5/6/2019 at 4:17 PM, relevante said:

The check engine light just came on in my new GMC with just over 2k miles on it. I just towed for the first time yesterday, but not a heavy load (definitely under 3000 lbs). I pulled the codes just now and got:

U0101 Lost Communication with TCM

U0129 Lost Communication with Brake System Control Module

I'm probably going to have to take it in to the dealer, but first wanted to see if this is a common issue or if there are any relevant bulletins or recalls out first, just so I can go in well-informed.

Thanks.

Hey partner, I get those codes everytime I remote start my truck with it hooked up to the trailer. Considering it a glitch.

Sheck · September 9, 2019

I too received codes U0101 and U0129 when pulling my empty toy hauler, about 6,000 pounds. The code went away after detaching the toy hauler. I have an appointment to take it to the shop for the software update. It was new in March, so under warranty.

Edited September 9, 2019 by Sheck
fixed typo

splatmatt · February 11, 2020

I've been seeing these codes show up on my Bluedriver OBD II code reader even after today's most recent recall that refreshed the EBCM.

If anyone has a fix for this I would appreciate the info - dealer is clueless in the matter.

Here is the summary:

Quote

Make: Chevrolet Year: 2019

Odometer: 2,140 miles

----Electronic Brake Control Module Codes Scan Report---- 6 Electronic Brake Control Module Trouble Codes:
1. U0140
Lost Communication With Body Control Module

2. U0100
Lost Communication With ECM/PCM "A"

3. U0101
Lost Communication with TCM

4. U0131
Lost Communication With Power Steering Control Module

5. U0151
Lost Communication With Restraints Control Module

6. U0146
Lost Communication With Gateway "A"

****Update

well, dealer said codes were history codes. Flashed ECM and reflashed EBCM for second time under latest recall. Performed a “complete history wipe” whatever that means - not sure how that is different from clearing codes. But I had to go back this morning for a B1517 as they left some connections loose.

Now I have driven 60 miles (since this morning) and 0 codes and transmission feels very smooth. Fingers crossed.

Edited February 13, 2020 by splatmatt

brianf60 · February 13, 2020

I had the MIL on. U0100, U0101, U0146 and P25A2. The light went out before I could get an appointment with the dealer and didn't feel like driving all that way to hear the "well we don't see anything wrong" BS and then I saw the recall for the brake module and wonder if they are related. I will try to get it in soon. Keep us posted.

WwRGSwW · February 16, 2020

Im getting U0100, U0101, and U0146 after hooking up my trailer today. Issue is not going away after removal of the trailer. I removed the neg battery cable for a extended period of time, code still shows. Cant clear it using my obd scanner either.

Good to know its most likely a false alarm. Ill take to the dealer later in the week.

splatmatt · February 17, 2020

Well it has been around 500 miles since EBCM firmware was applied and the dealer performed a history wipe.

One thing I noticed is MPG is about 1.5mpg better and the voltmeter on the dash is always riding above ~14.4V. After the update it now seems to behave more typical to the GM regulated voltage control system and zero codes including all of the modules.

**** issues are back again... dammit

Edited February 28, 2020 by splatmatt

Dalton Delogu · February 19, 2020

On 2/13/2020 at 3:35 PM, brianf60 said:

I had the MIL on. U0100, U0101, U0146 and P25A2. The light went out before I could get an appointment with the dealer and didn't feel like driving all that way to hear the "well we don't see anything wrong" BS and then I saw the recall for the brake module and wonder if they are related. I will try to get it in soon. Keep us posted.

Have you went and seen the dealer? Just had all four of these yesterday and the light was also gone after next day. Are you having any braking issues ?

brianf60 · February 20, 2020

I haven't been able to get it to the dealer yet. I'm not experiencing any noticeable issues with my brake. If I had I would just get it towed.. The MIL has not come back on in over the week either.

WwRGSwW · February 20, 2020

Im going to add, mine cleared its self after 24 hours. (OBD Scanner would not clear it)

Elpresidente · February 23, 2020

Has anyone found a resolution to this yet?

i think I have two different issues. The u101 and u100 and u101 and P25a2 issue. Had this twice. First time was to far from a dealer. Second time it was Sunday and the dealership was closed.

yesterday I had just p25a2 code only (none of the original ucodes) which might be the brake module; a software release was released for this in December. But it had bugs and caused problems with power steering. Now a second software update was released about a week ago.

https://www.autoblog.com/2020/02/11/gm-brake-software-recall-silverado-sierra-ct6/

these show different symptoms and with a high probability are different issues. Did anyone get any real/solid/effective or practical information out of GM on the ucode issues. There are about 4 different threads out there so probably hundreds of people have had this.