Lost Communication With TCM, No Speedometer, Power Steering Message - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 14 (permalink) Old 06-19-2017, 06:33 PM Thread Starter
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Lost Communication With TCM, No Speedometer, Power Steering Message

Hi all!

Bit of an introduction: I'm a college student with very little experience in car maintenance. I changed a tire once, and that's about it. But I'm willing to Google things and get my hands dirty, ha.

So last Monday, I bought a 2005 Chevy Cobalt Coupe from a coworker (my first car!). I had my car-savvy friend take a look at it with me, and he said everything seemed good. I hadn't driven it much till Saturday, when I finally got plates on it. Later that day, I took it out on the highway, and everything seemed fine.

Then the DIC popped up with "POWER STEERING" and my speedometer stopped working. Power steering seemed fine, although maybe a bit stiff? I turned around, and on the way back I noticed it seemed to not shift gears up as much as it should. I borrowed my friend's OBD-II scanner and it came back with a U0101 code, lost communication to transmission control module. I talked to the guy I bought it from, and he said that had never happened to him. I asked him about the power steering recall, and he said he had never received anything about it. I checked the VIN on Chevy's website, and there are no outstanding recalls for the car.

So I've been doing a lot of searching, and found a decent amount of people experiencing the same problem. The most common solution people mentioned was grounding the TCM to the chassis. That didn't work for me. I also checked all the applicable fuses, jiggled the BCM and TCM connectors and looked at them--they all looked fine. I also disconnected the negative terminal of the battery and let it sit for a while; no luck there, either. Clearing the codes got rid of the power steering message for maybe a minute, but it came back.

The next two things I'm planning on trying are cleaning the ground bolt for the TCM (G105), as that was suggested in this thread, and looking at it, it is a bit rusty. And then I was going to try pulling out the after-market stereo the previous owner installed, since someone mentioned there's a connection between the stereo and the car's computer (plus, the power to the stereo is a bit sporadic anyway).

So.... does anyone here have any suggestions for what to try? I haven't taken it to a shop (judging from others' experiences, it doesn't help much and is expensive--college student here ), but I'm willing to work on it and I have some other, more experienced friends who could probably help me out.

Thanks!!
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post #2 of 14 (permalink) Old 06-20-2017, 04:31 AM
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Pull the 2 greyblue connectors from the BCM and reseat them several times then go for a spin. If your problems are gone try a little dielectric grease.

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post #3 of 14 (permalink) Old 06-20-2017, 04:26 PM Thread Starter
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No luck... I tried reseating each of the connectors probably about six times. Still get the power steering message and no speedometer. (I assume the code's still there--I don't have the OBD-II adapter on hand.)

Last edited by isaac; 06-20-2017 at 04:50 PM. Reason: added info about code. Also, grammar
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post #4 of 14 (permalink) Old 06-20-2017, 05:06 PM
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Okay, now try re-seating the PCM/TCM fuse in the BCM or replacing it alltogether. it will be a 10 amp red fuse top left corner. These sometimes pit. This fuse is for the communication between BCM and all other CPU's and in my opinion not identified properly on the BCM block. Very misleading.


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post #5 of 14 (permalink) Old 06-20-2017, 05:58 PM Thread Starter
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I believe the fuse is fine. It looks like this:

(as do the rest of my fuses I've seen)

Just to be safe, I tried swapping it with my windshield wiper fuse (since I know those work, ha) and still no results.

Last edited by isaac; 06-20-2017 at 06:10 PM.
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post #6 of 14 (permalink) Old 06-21-2017, 02:23 PM
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Only other thing I can think of is a frayed Communication wire in the harness. It will be a dark green wire.
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post #7 of 14 (permalink) Old 06-21-2017, 03:14 PM Thread Starter
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Alright, I'll go out and visually check those in a few minutes. When my friend gets back from work, I'll probably see about checking it with a multimeter.

If that doesn't turn up anything suspicious, would you recommend I go to an independent mechanic or a Chevy dealership?

Thanks!

---------- Post added at 02:14 PM ---------- Previous post was at 01:57 PM ----------

I can only see a couple of inches of the wiring without taking things apart, since the wires go into the console/engine pretty quickly... Is that alright or should I dig a bit deeper?

Last edited by isaac; 06-21-2017 at 06:49 PM. Reason: survived the drive to autozone LOL
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post #8 of 14 (permalink) Old 06-23-2017, 03:59 PM Thread Starter
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Alright, took it to a mechanic and they told me the problem is with the TCM itself. Chevy wants six hundred dollars to replace it, and they don't seem willing to reprogram one if I bring it in.

If I can't find a TCM cheaper, I'm thinking of doing something like
and manually controlling the solenoids in the transmission. Does anyone have a pinout for either the TCM, or the connector that goes into the transmission, so I know where to wire things up?

Thanks,
Isaac
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post #9 of 14 (permalink) Old 06-24-2017, 06:29 AM
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How in hell does the TCM affect Electric steering and instrument panel. Something is fishy here.

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post #10 of 14 (permalink) Old 06-24-2017, 10:21 AM Thread Starter
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I dunno. My thinking was that I think the speed output goes through the TCM to the speedometer, and the power steering also uses that to adjust based on how fast you're going?

I'm going to a scrap yard today, going to pick up some wiring in case I do try just dealing without a TCM. Might also see if I can pick up a TCM, cross my fingers and pray it works. Lol
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