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Ok, so I'm new here and my wife and I recently picked up an '11 Acadia SLT2. It's high mileage 202k but she was a company vehicle and had good records for regular maintenance. It was dirty and needed a good detailing but all-in-all we got it for a song. That was about two months ago and we've been happy so far. Now, this!

We went to pull out of the driveway the other day and it was barely creeping along and the check engine light had kicked on. I have a cheap code reader and so I pulled it out. I had two codes initially. P0700 and P0430. I cleared them but kept getting new and different codes. P0026, P025e5, P0007... I decided that the issue might be electric/grounding given the bizarre range of non-repeating codes. I parked it and went about looking for a grounding issue. I looked through some info online and found that one location on the B-pillar of the passenger side that looked like a possible culprit. Disconnected the battery, loosened the ground, cleaned and reassembled. Viola! Problem gone and I congratulated myself.

A few days later, the P0700 returned. Along with a couple of new codes. U25e5, U2524, and U2565. The U codes pop up one at a time and but are always accompinied by the P0700. This time they don't seem to want to clear by unhooking the battery and fiddling with the groundings. I was reading the great writeup by @stepel on the TCM issue and wonder if that's what I have going on. However, I wanted to get the input from this fine community before I tear the transmission open, and start laying out for parts.

One additional related question. Does anyone have a recommendation on a bi-directional ODB diag tool for active testing that won't run several hundred to several thousand dollars???
 

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So the "U" codes weren't making much sense to me so I borrowed a different diag reader from the NAPA here. It too pulls the P0700 code but it also pulls a P0657. At least this one makes some sense, and my other reader doesn't see it at all. Reading about P0657 the info I found indicates that it's low voltage on actuator supply voltage A. General googling indicates that this is likely related to a transmission issue. So far that seems to be making sense!

So it seems I need to investigate this circuit "A" but I don't know where to start exactly. Does someone know where the FSM for this vehicle might be found? I found an 08-10 manual on this forum before, but since this is an '11 I don't want to chase my tail on poor info. Ugh, there's snow coming in tonight too! My wife was so hopeful that I'd have this sorted out today :( She does hate driving that van of ours in the snow! LOL
 

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Welcome to the forum.
Since OBD II is the standard for these vehicles, model year shouldn't be an issue. Also, few significant changes were made to the transmission through the model run (a change of TEHCM in 2013 is the most significant). The downloadable FSM in the forum will likely be helpful with resolving the problem.
 

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Thanks for the reply speleos! That FSM I downloaded from a link here says it is for the Buick Enclave 08-10. Do you think it should line up with ours, or is there another FSM you had in mind?

The snow that was promised did not disappoint! I have her in the garage right now but it's frickin' cold out there so I'm not making fast progress. On an off chance I pulled the airbox out and pulled the TEHCM and ECM connectors to clean it and then reseated them. No joy there, but worth a shot. What I'm thinking next is to pull the drain plug on the tranny and then pop the TEHCM out to inspect those pressure switches.

I'm going to go through the FSM but I confess I'm not sure how to navigate them very well. I have been able to sort out what they are saying when I read it, but I haven't found the diagram for that connector yet.
 

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Thanks for the reply speleos! That FSM I downloaded from a link here says it is for the Buick Enclave 08-10. Do you think it should line up with ours, or is there another FSM you had in mind?
Enclave and Acadia are nearly identical vehicles when referring to basics.
 

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Well, that took more time than I thought! Taking care of the kiddos might have something to do with how long it took! So I have the TEHCM out and the pressure switches look fine... :(

So. I'm not sure where to go next from here. I'd love some feedback from the community. What should my next steps be? Do I button the trans back together, or should I be doing anything or checking something else out before closing it and poring in the 50ish bucks in fluid back into it?

BTW, the fluid did look pretty gross. I did find a sticker inside the glovebox that said it had the transmission serviced at just after 100k. (No indication if it was a flush, or just a drain and fill)
 

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Ok, so I've put the trans back together. Not that I was expecting a miracle, but it is still behaving the same way... Boooo! ;)

We have a local mechanic that was good enough to do some diagnosis with his ODB system and didn't charge! He did get the same P0700 but got a P0658 code instead of the P0657 that I received. That seems to be related to the same circuit for both codes but the 58 indicates high voltage vs the low voltage on the 57 code I received before. He also pulled a P050A code that is for Idle Air Control System Performance, but I'm less worried about that one unless someone here can tell me they think it's related to the larger Trans issue. The mechanic said he also thought it was the TEHCM, but said his first suspect would be an issue inside the wiring harness. This leaves me to look at the wiring going into the passthrough TEHCM connector, but I still don't have a solid understanding of the wiring schematics. Looking at the wiring information diagram from the FSM I downloaded there seems to be two pins that are attached to ground G110 in the harness on pins 1 and 18. However, I've not yet been able to find a description of where the G110 ground is, nor have I been able to ascertain which pin is #1 in the harness or how the numbering works.

Onward and upward though! As always, any input would be greatly appreciated.
 

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BTW, the G110 ground is used for comm to/from ECM/PCM and transmission. Might want to pay attention to condition of connectors at the other end, too. The ground may originate from one of the other control modules.
 

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#1 and #18 are black with a white stripe. G110 is shared with the A/C clutch, MAF, ECM, Trans, Brake booster and a bunch of relays (rear defrost, crank, fuel pump, trailer backup, ignition). G110 is located at the right rear of engine, mounted to the rear cylinder head.

Connector numbering: G110 is number 3 in this image:
I've been navigating GM FSMs for a while. They're tricky. Good luck!
 

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One more thing: I looked up your codes and there is no such thing as P0657, P0658, or P050A for this vehicle.

Here is what it says for P0700:
This diagnostic trouble code (DTC) indicates that an emission related transmission DTC set in the transmission control module (TCM). The engine control module (ECM) receives the TCM information over the serial data circuit. The ECM turns ON the malfunction indicator lamp (MIL) when the TCM sends a message over the serial data circuit requesting MIL illumination. The DTC information for the ECM will only display DTC P0700, but the freeze frame/failure records data will display the transmission DTC that set.
I think you need to do more digging with a better scan tool.
 
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