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2015 Limited Baffling Transmission U0101 Code

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electrical issue service stabilitrak tcm transmission code u0101
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17K views 80 replies 9 participants last post by  GrizChev  
K
#1 ·
So I've been stumped by this U0101 code.. and I'm at my wits end trying to troubleshoot it. Here is the backstory.
History of the Vehicle:
  • The car is a 2015 Impala Limited base model I believe. Has the 3.6 V6 and the 6T70 trans
  • I purchased it used from Offer up on 2/4/2024. Car had no major issues besides a noticeable hard shift from 3rd to 4th gear while driving & a delayed engagement from park to drive. I was in need of a car so bought it anyway. Runs strong and no issues in any other gear while driving.
  • Up to this point I had changed Engine Oil / Filter, Changed Transmission Fluid (Old fluid was VERY dark), Replaced Spark Plugs & Replaced Air Filters.

Start of the Issue:
5/25/2024
Being that the transmission fluid was so dark I decided to change it again after a couple thousand miles of driving. I change the fluid, the car starts and drives fine no problem. I proceed to wash the car and call it a night. The next morning I go to start the car up and I upon starting the Check Engine Light is illuminated, the gear selector circle is missing, the Stabilitrack / traction control message shows on DIC, the car high idled to around 2-3k rpm. I immediately shut it off wondering what the hell was happening. Plug in a scanner and see the U0101 code pop up. I watched a few quick videos and saw that there is a common issue with the TCM connector being dirty. So I left it connected and used compressed air to blow on and around the connector. Unhooked the negative side of the battery for a couple mins, reconnected, start the car and all is good. I drive away no issue.
Image



6/12/2024
My gf is driving the car to work in the morning (Somewhat dewey / wet morning) she calls me on her way to work saying that the issue is happening again, this time while she was driving. She pulled over and I told her to leave it running (While I planned on driving over to her) After a few mins she calls back saying all the lights went away and the car seems to be normal. I brush it off but know that there is somthing fishy going on with it happening again.

7/4/2024
Go to start the car in the morning (Again a misty/wet morning) same issue occurs on startup. All lights pop up, message on DIC, no gear selector. I attempted to move the car anyway and put it in reverse and it slams it into the reverse gear making a loud CLUNK. I through it into drive and give gas and pull it back into the driveway. Shut the car off and leave it for a couple weeks while away on a trip.

7/16/24
Finally back at the car and now start to diagnose the issue to determine what the hell is going on. I've read through forum posts, Facebook posts, watched almost all YouTube vids on the subject and read the service manual steps. Here is what I have done so far.
  • Pulled the TCM connector off the trans and used electrical connector cleaner to clean both female and male side of connector. (Cleaned it about 5 separate times to ensure no residue of trans fluid / debris) The connector was relatively clean when I pulled it off. No bent pins on male side that I could see.
Image
Image

  • Removed black cover on TCM connector and checked wires for damage/pinching. (No damage visible.) I also pulled wires out of the loom about halfway to inspect and all looked good.
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​

  • I pulled out the multimeter and follow along with the Service Manual steps. By completing the following
    • Test the Red/Wht B+ wire for Voltage: 12.5V
    • Test the 2 blk/wht ground wires for Continuity to negative post of battery: 1.1Ω (Service manual states under 10Ω is good)
    • Test the pink IGN wire for Voltage: 12v (When key is in run position)
    • Test the blue Acc Wake Up Serial Data for Voltage: 11.3V
    • Test resistance across both pairs of High Speed Serial Data wires: Pair 1: 121.8Ω Pair 2: 121.8Ω (Service manual states under 130Ω is good)
    • I should note that I attempted to move the wires and loom around while testing to see if there was any loose connections. Nothing abnormal found.
      Image

  • I pulled the battery and had it tested at an auto store. That tested good.

  • I applied a small amount of dielectric grease to the female side of the connect and plugged it back in.
I attempt to start the car and the same issue still stands. Throws code U0101 and all the lights and messages pop up along with no gear selector circle.
At this point I figure all signs point to the TCM being bad, but with so many other people having this issue and it being related to wiring along with the somewhat intermittent issue I am reluctant to purchase a TCM and swap it because I feel like it won't be solving the issue. I have also read that the TCM rarely goes on these so I figure its likely something else.

I am running out of ideas to test and am leaning toward purchasing a refurbished TCM off of eBay to test it. But I wanted to see if anyone on here has any ideas before I pull the trigger.
 
R
#65 ·
Dealership in Southern Pines diagnosed as bad TCM, but I had them send me a photo of the connector and it looked like crap. I also went there to discuss it and when I arrived the connector had been reconnected and vehicle had been moved, the technician was explaining his diagnosis and I asked him for the key, started the car and viola the TCM was working. I told them to just re-pin or replace the connector. Grudgingly they agreed. After replacing it (4 hours labor and $50 part=$700) the issue is resolved. To replace the TCM was quoted at $2700 and would not have solved the issue. I saved $2000.
 
K
#67 ·
Great to hear you got it figured out! My intuition is leading towards any of these error code or issues being the female end of the connector as the culprit. Good info for future owners who run into these issues that the dealer can't diagnose.

Let us know if you see any issues arise again.
 
#68 ·
Rick Stievenart said:
Dealership in Southern Pines diagnosed as bad TCM, but I had them send me a photo of the connector and it looked like crap. I also went there to discuss it and when I arrived the connector had been reconnected and vehicle had been moved, the technician was explaining his diagnosis and I asked him for the key, started the car and viola the TCM was working. I told them to just re-pin or replace the connector. Grudgingly they agreed. After replacing it (4 hours labor and $50 part=$700) the issue is resolved. To replace the TCM was quoted at $2700 and would not have solved the issue. I saved $2000.



Does anyone have a handy diagram for what the part number is for that full wiring harness between the TCM and ECM and getting the whole thing replaced instead of the connector (and all that labor charge??)
 
#69 ·
2014 Impala LTZ 3.6 right?

And this part is your question?:

"Does anyone have a handy diagram for what the part number is for that full wiring harness between the TCM and ECM and getting the whole thing replaced instead of the connector (and all that labor charge??)"

Are you sure you don't want to start your own thread. I can do that for you. Let me know.

.
 
#70 ·
Keeping separate, I think the interconnect is not a single cable set direct. But go to:
Www.charm.li to see the cables.

I don't believe they are in the parts manual in my help files but when able I'll look or you can if you want.
 
#72 ·
Ok my bad when I looked it up all 2012~2020 Impalas using the 3.6 came with 6T70 including both body styles. The subject parts appeared to be the same. If they are not then my bad I should have dug deeper. 😊
 
#78 · (Edited)
The first thing is to identify the plug for manufacturer and type, from which you can identify the terminal parts, and that will detail how pins are affixed to the wire ends and how pins capture into the plug (and same for matching half of the connector.

I don't recognize the connector shown in Post#66 from last summer. Nobody else has commented with ID either.

I realize different vehicle years and models might vary.

I'd like to see this solved.

My take, based on that recent pictured connector plug, which at-a-glance has many missing female terminal fittings (that pins plug-into) and that needs proving to know what's missing.

There's sometimes little release tools needed to match. Sometimes the new terminal snaps in. Sometimes a tool is needed.

Sometimes releasing the connector releases all the terminal ends. Other times each has its own release.

Sorry can't know what is involved until parts are udentified. There's dozens of unique bits. But most transmission shops would know and would have terminal ends.

ADDED:
THE ONLY POTENTIAL GM CONNECTOR FROM CHINA IS 88988938 HOWEVER ITS ONLY AVAILABLE AS AN 80-PIN SHELL. IT WILL NOT WORK UNLESS FITTED WITH WHAT APPEARS TO BE A SPECIAL 20-TERMINAL FEMALE PLATE AND WITH HOT FLUID SEALS. THE 20-TERMINAL FEMALE CONNECTOR ACCEPTS THE 17-PIN MALE CONNECTOR ON THE TCM VALVE BODY (3 MISSING PINS) AND THE TERMINALS (PINS AND RECEPTACLES) APPEAR TO BE MOLEX BRAND. SPECIAL TOOLS. AND A MAX 30 WATT SOLDERING "IRON" TO TIP THE (SEVENTEEN?) 18~20 GA COPPER CONDUCTORS.

THERE ARE ALSO KNOWN VARIANTS, NOTABLY IT TURNS OUT MUCH OF THE WORLD GOT IMPALAS IN AT LEAST 2011 FITTED 3.5 3.9 AND 6T70 WITH 17-PIN CONNECTOR WITH DIFFERENT SEALS AND TERMINALS. THE ONLY SOURCE FOR ALL OF THESE IS CHINA. AND THEY DON'T SEEM TO OFFER KITS WITH PARTS NEEDED FOR 17 OR 20 TERMINALS.

SEPARATE THERE IS THAT COMPUTER ADAPTER I PICTURED EARLIER ALLOWING DIRECT PLUG-IN FOR DESKTOP PROGRAMMING THE TCM. THAT IS ACTUALLY A TWO-WIRE DEVICE. IT HAS THE 20 TERMINAL SET-UP ON ONE END AND A COMPUTER PLUG ON THE OTHER. WON'T HELP. AND ITS ONLY PART OF WHAT IS NEEDED TO DESKTOP PROGRAM. THE OTHER PARTS ARE ACDELCO AND DISCONTINUED.

LOOKS LIKE THE ONLY ACTUAL SOURCE OF REPLACEMENT CONNECTOR IS SALVAGE YARDS. THEY WOULD KNOW INTERCHANGE. THE INTERCHANGE PROVIDED EARLIER HAS NOT BEEN PROVEN BY ME IT'S UP TO YOU. THAT MEANS VERIFY MOLEX TERMINALS TOO.

I DON'T SEE ANY OTHER AVENUE. HOPEFULLY OTHERS WILL HAVE INFO TUCKED AWAY.
 
#81 ·
I updated my Post#78 to report details, no luck finding the 6T70 TCM/ValveBody connector. IMO any pictures of connector needs to be real-world pictures by members of their actual connector plug. There are too many generic images used by sellers. There are too many factory variants. Better to (1) compare at salvage yard and (2) verify if parts are MOLEX then buy terminal ends etc at Grainger or a large auto parts store where they can identify.

Separate: its possible all the terminal ends are fine in this case (pushed on plug and temporarily fixed trouble). Could be just one pin is loose or was not factory installed correctly. Un-pinning the entire plug might be an option but it's a major pita. I don't know if this female side can unpin just one terminal. No internal images and no technical sheets with pinout and details. This smells like on-the-fly bin parts were used and bins were refilled with what ever was available that worked.

..
 
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