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:
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.
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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.
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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.
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.
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.
- 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.
- 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.
- 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.
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.
