Multiple TCM Codes

Tiny
MJP9348
  • MEMBER
  • 2005 CHEVROLET 2500
  • 6.6L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 242,000 MILES
So, I have a transmission problem and my truck is throwing 22 TCM codes, I will give a quick jest of the problem.

So, the problem started out about 8 months ago - wouldn't lock into fifth gear and when mashed on the pedal the passing gear (dropping down to pass) wasn't happening, slow and sluggish.

Following that 1 month later after 30 minutes of driving the truck would just shift into only third -fourth gear and wouldn't come out of 3-4 gear unless it was put back into neutral or park and reverse. Then you could start to drive it again and in a matter of minutes, back to only 3rd and 4th gear.

Fast forward, it sat all winter, because I don't have a garage to get it into.

This Month (May), now that the weather is tolerable - dropped the trans pan - no debris (or material)- fluid is a beautiful red - replaced all the solenoids with OEM and wire harness, but during the investigations under a plate (Trim solenoids) there are two springs, one was broken into three pieces. Replaced both of those springs as well as the Psm and the MLPS switch on the outside of the transmission, plus a new wire harness (found mine was leaking trans fluid during the inspections).

So, none of this stuff was replaced by me or anyone else since I had purchased the truck 8 years ago, so I figured now was the time to do it since I'm dropping everything down.

(Replaced all filters as well for transmission)

Well that fixed nothing.

First it was shift inhibited when I finished up, so
I replaced that electronic lock in the steering column (no change).
checked all the fuses, (they are good).
Fluid is full.
Checked the pins on the TCM (seated tight).
relearned Transmission.

I reset the main TCM harness and cleaned it up, and the Shift inhibited went away, I was able to drive the truck and it was moving, like I haven't felt in a while, had power, nice shifting, everything was great in the 20 minutes I drove it.

Wife jumped in it and drove another 20 minutes and it went out of gear and then automatically locked into fourth.

She would put it into park, reverse works as it should, put it into first, and within 3 seconds would lock into fourth. You hear the transmission, just change gears at a standstill to the fourth. Messed around with it a bit more, cleared the codes, shifted through all the gears, but after a few seconds, automatically into fourth and locks. Run diagnostics and found 22 Errors.

It's sounding like a communication problem, but I am not sure. I keep thinking the TCM is messing up judging by the codes she is throwing at me. But again I am unsure.

Anytime you start it up throw it into reverse - no shifting issue - neutral - no problem put it into Drive and she will sit in first gear for 5 seconds then you hear it shift into fourth and lock, just sitting there idling not driving with your foot on the brake.


I am not asking you all for a miracle but some trouble shooting steps to start following, I am asking with everything that I described, does it sound like the TCM is stepping out on me and needs to be replaced? As Much as I want to purchase and slap a TCM I don't have a lot of money to just parts change to hope for a fix.

Mike L from DuramaxDiesels. Com said this : The problem is you through every code in the book. Every gear is slipping, you have speed sensor codes, you have tie up codes (2 gears at once.) You have valve body codes. Start with a known good TCM and see what codes come back. Then move on to the valve body.


So, I am asking for your guy's opinion if buying your TCM is the way to go with this?

Thank you much. Mike
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Monday, May 30th, 2022 AT 10:27 AM

14 Replies

Tiny
MJP9348
  • MEMBER
Cont. For some reason the pictures of the codes did not upload with original question. Here are the current active codes hard codes.
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Monday, May 30th, 2022 AT 10:33 AM
Tiny
KEN L
  • ADMIN
Yes, with this many problems it is pointing toward the TCM needing to be replaced. Here is the location and instructions on how to do so in the diagrams below. Also, you can do a CAN scan to confirm the failure before you begin. This guide and video will show you how:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.
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Monday, May 30th, 2022 AT 6:04 PM
Tiny
MJP9348
  • MEMBER
I appreciate the reply Ken, let me get to work on it and as soon as I can get a TCM to put in it, I will follow up. Thanks a bunch.
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Tuesday, May 31st, 2022 AT 4:08 AM
Tiny
MJP9348
  • MEMBER
Follow up, I got the TCM back, the guys said it tested good. I have made a wire harness that connects the trans harness at the pan back to the TCM connections, and so far out of 10 wires on the red side I found 2 pins ohming at 1.0 which is too high, and 1 wire with no continuity. So My question is, what are the pins that connect into the TCM connector? I have done some looking and I haven't come up with what size and make the individual pins are. I can't justify spending six dollars on three of them through a diesel store either, when you can buy them by the 10's -20's for that much.
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Thursday, June 9th, 2022 AT 5:21 PM
Tiny
KEN L
  • ADMIN
Nice work finding the issue. here is a TCM wiring diagram, so you can see how it works and what the wires go to in the TCM, also a guide to help test the connections as well.

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what you find.
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Friday, June 10th, 2022 AT 9:12 AM
Tiny
MJP9348
  • MEMBER
Hi Ken, well, I made a 16g x 10 wire harness x2 along with a male end running into the transmission, fixed a couple wire ends, as I mentioned above, after taking them apart, they were more superficial, but still, I fixed them.

I checked the continuity of the whole harness. TCM to transmission, to fuse box, to under dash, you name it, I followed it. All ohmed out at.3 to.4 at the highest. So, my trouble shooting skills from when I used to be a heavy equip tech kicked in finally and said "hey let's check the TCM" mind you I sent it out, and got it back, the people claiming they tested it. So, grey connector side, TCM out of the truck, on a flat surface, I probed 1 pin, and then checked it across to red side, and yes. Over 1 ohm. So, I managed to find multiple pins, which crossed over to the red side, and yes, I can see that happen to a point, but I shouldn't have a dead short on case when testing the pins. Red and Grey side, I had multiple pins that ohmed out as a short to housing of TCM. 1.0ohm on up randomly up and down to no less than 1, I think I had a 500ohm there at one point.

But, with that said, ground is fed to the TCM by plug from the body. The magnesium case or pot metal or whatever the case is made out of shouldn't show continuity to the housing of the TCM correct? Anytime working on equipment, if I had a short to housing ohming connectors and pins that was the last nail in the coffin to confirm bad ECU or ECM.

So, if you can read this and let me know your thoughts, I would really appreciate it. Thank you for all the assistance.
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Monday, June 13th, 2022 AT 4:08 PM
Tiny
KEN L
  • ADMIN
The housing of the TCM can be grounded yes, the ohm reading sounds normal, but I was looking at the codes again and it could be the input shaft sensor is not working correctly. Or the transmission may be slipping. We can try the sensor first. Here is the location. Check out the diagrams (below). Please let us know what happens.
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Tuesday, June 14th, 2022 AT 10:13 AM
Tiny
MJP9348
  • MEMBER
Hi Ken, I already replaced the output speed sensor the other day. Here is a crude video of the TCM test. We'll as pointed out by someone else, the transmission can't slip if it's not in gear and throw codes about all the gears being incorrect ratios. Basically, what I was told was, how can the TCM determine gear ratio, without being driven? Or throw a multitude of codes, just by putting it in drive without moving. I put it in park, reverse, neutral no codes. The moment I put in drive within 3 seconds I have 30 codes that pop up and basically throws every single code the transmission has? And locks into 4th.
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Tuesday, June 14th, 2022 AT 10:31 AM
Tiny
MJP9348
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Also, I am pretty sure you cannot ground that TCM, due to this symbol, that's the symbol for ground with a big circle and cross out on it.
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Tuesday, June 14th, 2022 AT 10:34 AM
Tiny
KEN L
  • ADMIN
Thanks for the video, it sure sounds like the TCM is bad. I have seen where the PCM goes bad and effets the TCM but it's rare.
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Tuesday, June 14th, 2022 AT 10:39 AM
Tiny
MJP9348
  • MEMBER
Hi Ken, quick follow up, and great news, and hopefully you and other people can help pass this knowledge with other people in my position.

1- replaced TCM with junkyard (eBay) TCM - 01 to 05 TCM does not need to be programmed or vin flashed, it will work as a plug and play TCM.

Unless you wanted to be picky to having everything match then you can have it vin encoded, but, I purchased one off eBay for $150 dollars, plugged in. 1 TCM code. P0872 stuck solenoid. It's my only code for the TCM instead of the 25 plus I was getting (i have to work outside so it looks like rain and I will get to it in a day or so)

I am so glad I didn't get soaked on buying a $750.00 + dollars refurbished TCM.

2- the other code I am getting is the U1096 - unable to communicate with the dash, not sure what to do about that one yet, because that was in the list of codes as well. Figured I would get to this stuck solenoid first.

Any suggestions on that code? U1096

Ken thank you for sticking this out with me, and throwing some educated suggestions, and giving me some really helpful input and schematics.

I will follow up after I drop the pan again.
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Wednesday, June 22nd, 2022 AT 9:25 AM
Tiny
KEN L
  • ADMIN
Hmm, I have seen the instrument clusters go out causing the communication error U1096 and this can cause the TCM to seem bad as well, that is the problem with CAN systems, one controller can affect another. This is why I like to do CAN scans. Let me know how it goes.
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Thursday, June 23rd, 2022 AT 9:38 AM
Tiny
MJP9348
  • MEMBER
I agree, but to go from 25 plus codes to 2, I'll take that any day of the week. But I will follow up and let you know what I find, it might take a few days.
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Thursday, June 23rd, 2022 AT 9:50 AM
Tiny
KEN L
  • ADMIN
Yes, we are getting closer, let me know.
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Friday, June 24th, 2022 AT 9:25 AM

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