Tccm compatibility clarification

[Elizabetty]

Hello. I saw on this site...

Compatibility of different TCCMs for 4x4 Envoys, Trailblazers, etc.

Hi, all. I have a used 2002 Envoy SLE (4.2 I6) that is in great shape, except for no transfer case control (surprise surprise...) At any rate, I get the classic "lights on control switch light for a few seconds at start up, then turn off, with check 4WD light on dashboard". So, the switch...

gmtnation.com

...discussions about using a tccm from various GM compatible vehicles across a few years. When shopping for a replacement, I get conflicting info. There are used ones that show my 2002 as compatible but if I go to a GM part site, it says what I'm looking at is not compatible and it directs me to something else. I pulled the wiring schematics and while I do see some differences, they are wire colors and the atc fuse amperage. The fuse in mine is a 25a and the fuse in the 06 on the diagram is a 30a. Perhaps this is why not compatible?

Mine: 15085386
Suggested replacement: 12590220
Found: 24233673 from 2006 TB listed by seller to fit 2006-2009 TB and then similar date spans for Envoy, Rainier etc ------ I found other sellers of the same part number marketing it to fit my 2002 all the way through 2009. The GM part site for compatibility and replacements says it will not fit and points me to the suggested replacement above.

Is this amperage part of the issue and should I stay away from this replacement part?

 

[TJBaker57]

Mine: 15085386
Suggested replacement: 12590220

My 2002 is also 15085386.

For experimental purposes I have used ALL of these in my truck:

12580060
12584313
12590220
12577480

Every one of them worked.

I still have them all and I use the original 15085386 from the factory build in October of 2001.

 

[Mooseman]

The original 2002 TCCM had a defect where it can fail unexpectedly. Mine failed when it got below -20c. If it's working fine, you can leave it alone until it does fail. If you have an opportunity to grab one cheap at a pick-n-pull yard, go for it and keep it as a spare.

If it hasn't yet, it may never fail.

 

[Elizabetty]

Mine did fail. It doesn't wake up. I grabbed one from a junkyard today that happens to be the one I was questioning in my original post and I don't believe it is compatible based on codes I'm pulling now.

 

[Mooseman]

You can plug it in and see what happens. Only ones that would not be compatible are those from AWD (non-4x4) vehicles like the Olds Bravada, Buick Rainier, Saab 9-7x and the TBSS.

 

[Elizabetty]

Yep. That was my issue I think. Came from Envoy with AWD I believe. Not 100% sure cuz I went through multiple cars and had no phone service to learn about what I was pulling out of so I took some risks and can't totally remember. Figured that might have been the issue after more reading at home. (I creep on a lot of other threads and on another site where I see similar names posting on related topics to all my issues.) Sold me a throttle body that works great (I actually shorted mine out on accident. Note to self to be fully awake and alert next time I'm doing electrical work LOL) the TCCM, Map sensor, IAT sensor, and multiple pigtails as well as fuses and relays for 20 bucks. I said I'd take it and try it. Everything from the Envoy and a 4wd TB that could be compatible. For prices like that, I'm going to stop back there on Monday and go dig through some potentially part-compatible vehicles and grab a bunch of stuff to put in my "just in case" box since I have so many irons in the fire and I'm traveling so I can only work on things in tiny increments at a time. Makes it hard to solve something so I'm sort of just keeping it running while I make my way across the country. Next stop Illinois next week. Not sure I'm going to find a junkyard willing to sell me parts in bundles like that for another $20 bill so I almost feel like going back and ripping the harness out of the other Trailblazer (if it matches) to be honest LOL

 

[Elizabetty]

Shoot. Blonde moment. TCCM did come out of TB, 4wd, but 5.3l from '06. That's why it doesn't work I'm assuming. I don't think I even looked under the hood on that one and just saw it dangling under the dash and grabbed it since the driver's door was missing and I had a good view while I walked by LOL
Yesterday was a blur. Rows of cars and a lady wandering aimlessly....PS: I was the only lady there so it was definitely me with the aimless wander haha

 

[Mooseman]

4.2L or 5.3L doesn't matter. They're the same. Not sure if there would be a difference for the year but usually 03-05 would be safe to assume they would work.

Maybe it's not working because of another issue if it's doing the same thing as your old one.

 

[Elizabetty]

Actually, what it's doing is so over my head that I decided not to look into it too much when I only have little bits of time to do things.

Good to know the 5.3 doesn't make a difference because I saved the part and I'm going to eventually look into it now that you mentioned that.

It's definitely waking up unlike my original. However, it gave me a bunch of codes and some of them were front axle and encoder motor related. I don't have those same codes when the old one is awake. (I don't have the list in front of me right now to supply them so I'm just generalizing what happened.)

Without knowing why that might be happening, I took it out and assumed it must not be compatible until I have time to further understand. Perhaps it is compatible and the codes are correct and even though the old one is occasionally awake and does not give those codes, maybe it's s because it isn't functioning properly for the PCM to do so.

As I write this, another thought occurs to me. At the time it was plugged in, I had a different PCM in that I was troubleshooting on a whim that ended up not being what I needed for my setup. I purchased one from eBay that had the exact same part number information. It was cheap and I was curious. However, I'm thinking it was set up for a different gear ratio. I had speedometer issues tipping me off not matching actual speed and I think the speed is calculated based on wheel size and gear ratio but I could have taught all of that to myself incorrectly I suppose. I was under the impression an exact match would have the same RPO codes for gear ratio but perhaps not. When putting my original PCM in, my speedometer was correct again. Now that I have the original PCM in, maybe I need to try this TCCM again. I don't know if PCM for different setup would conflict with the TCCM. Of course, it could be as simple as I'm getting codes from this one because the other one simply wouldn't work correctly for the PCM to alert me.

 

[Mooseman]

PCM and TCCM don't talk to each other at all so that wouldn't make a difference. Maybe the 2006 isn't compatible or maybe the codes are valid for defects. Did your old TCCM ever work? If not, maybe you have other issues.

 

[Elizabetty]

PCM and TCCM don't talk to each other at all so that wouldn't make a difference. Maybe the 2006 isn't compatible or maybe the codes are valid for defects. Did your old TCCM ever work? If not, maybe you have other issues.

I was able to go in and out of four-wheel drive with my old tccm but I would be driving down the highway and it would randomly be changing where it was lit up with no prediction of when or why and different lights each time. I eventually could not use all-wheel drive, no light and no engagement, even though the light worked when turning the key on, so I thought it was a switch malfunction. Since I was able to use the other options on the switch, I figured the motor was fine and it had to be tccm related. (Same problem with different switch and could still use other 4wd options.) The best way I can explain it is that I could command it to do the four-wheel drive when I wanted it but until I sent that signal, it seemed to check in and out on its own. The best explanation I found online is that it doesn't like to wake up or it will randomly wake up on its own and start miscommunicating, hence the light randomness as well as occasionally going into 4hi, not just showing the light but actually doing it. If the crazy switch lights were the module waking up on its own with incorrect information at random times, then I was led to think it must be sleeping during other times which would mean bad tccm like so many others from '02.

 

[TJBaker57]

PCM and TCCM don't talk to each other at all

Actually, they do but I don't think that is really related here.

 

[TJBaker57]

would randomly be changing where it was lit up with no prediction of when or why and different lights each time

Textbook case of a failing encoder circuit. Often due to the encoder/sensor itself or poor connections as I posted about on my own 2002 not more than a month ago.

Given the right combination of TCCM oart number and calibration number I might be able to set you up with PIDs to be able to see the encoder/sensor return voltage and the selector switch return voltage.

 

[TJBaker57]

A TCCM that has disabled all shifting due to a fault detected in the system will have all the appearances of a TCCM that has failed to wake up. The indicator lights will be disabled (off) and the system will not respond to any actions until it is reset or the system fault is no longer there.

An encoder return signal voltage that is out of range is one such fault.