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TCCM Replacement How To

146K views 126 replies 48 participants last post by  akustoms 
#1 ·
I purchased my TCCM from GM Parts Direct. It cost about $200 Shipped.

Here is how you replace it.

First take off the panel under the steering wheel and the pannel that is below that



This is what you will see from under neath the blue clip goes into the TCCM there are 3 different plugs that clip in there. It is right behind the metal plate that you will see when you take off the pannel, It is all the way to the drivers side.


These are the 3 plugs after you take them out of the TCCM They unclip pretty easily but require a little contortion to get your hand up there to them. I am sure you could just take more stuff off but this wasnt too bad.



This is how they go in the TCCM. Note, you cannot put them in before you pop the new TCCM into its bracket. This is just so you can see the order of the plugs because you won't be able to read the label on the TCCM when you put it into place.



Clip the TCCM into its bracket, and install the plugs. The small black plug goes all the way to the passenger side, I labeled them in the drawing.



Put the dash back together, go to the dealer and get it programed.


any questions just ask here, don't PM me
 
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#96 · (Edited)
You sir are awsome!! Seems that I have more then 1 issue. First issue is my 0vdc on fuse 8 (both sides). Gona tackle that tomorrow and post back results


Edit: so I checked my 0vdc on fuse 8 in the front. Rookie mistake and metered to positive. Hence my 0vdc. That's all good. 12vdc present on fuse 8 :). Got into the tccm and check power going in on Orange wire and that's 12vdc. That's all good. Then I went to the tccm switch and I gots power coming in on brown wire at 12vdc. I also checked the LEDs to make sure they were not burnt out so I grounded each out separately and they all light up. So I'm at a loss?? I have 5vdc on my reference points and the switch meters out fine.?? It's prolly soothing I've over looked or it's something that the dealer might have to look into? I'll post back if anything changes?
Feel free to steer me in any directions :)
 
#99 ·
Just logged in to report on my story to get our 02 Envoy 4WD back.

Have an 02 that sat for 9 days when we were away on vacation, Came back and the battery was so dead, there wasn't enough juice to remove the key from the ignition when it didn't start. Had it jump started - the "Service 4WD" light came on immediately when the car started. So I came here to read up - tried the "pull fuse 8" to wake up the TCCM, didn't work - tried the "hold 4WD switch past the 4LO position", didn't work.

So following the wisdom written here, I called the bone yard to see if they had a TCCM - I was in luck, they had an 03 TB, $75 for them to pull it and $50 if I pulled it myself. Was the easiest $25 I every saved, the TB that I was to pull the TCCM from already had the dash panels and column removed - took all of 30 secs to unplug the TCCM. Got home and removed the 6 screws holding on the 2 dash panels below the column - reached up behind/below the headlight switch and pulled the TCCM and its little plastic holder out from underneath the metal dash frame - removed the 3 plug connections on the TCCM and popped in the one from the bone yard - put the dash panels back on - entire job took 14 minutes. The "Service 4WD" light was out, the lights on the 4WD selector were back on and the 4WD worked fine.

As noted in other posts, the model number on my 02 TCCM was 15085386 and the 03 TCCM was 12580060.

Thanks for the wisdom provided on this site!
 
#100 ·
My turn to wake up my tccm?

I have read the multitude of threads on our TCCMs. I still have a couple of questions I want to put out there before I make a move on a replacement (used one from a junk yard per Roadies advice on not needing reprogramming.)

1. It's an 04 TCCM which means it should be the updated one less inclinded to fail?
2. Is my TCCM about to go? Should I simply spend the $90 (with ship) and replace it; as I will need reliable 4HI (I dont use the A4WD as per Roadie rules) in the Maine winter (although it has been shocking warm of late)

I have serviced the transfer case as suggested in the Owners Manual and used dealer purchased Autotrac fluid. Lately my indicator lights on the switch sometimes do not illuminate at all? This is intermittent as I just went out for coffee and sure enough...worked fine? I also engage the selector to see if I could hear the actuator moving.....I could. I have also done the switch the switch a 100x thing to see if it helped....it didn't as the lights are still hit or miss.

I am tempted to just spend the $90 and be done with it...but of course wanted to bounce it off the forum first for any addtional insights. And to be sure I am addressing the likely cause. THANKS TO ALL in advance!
 
#101 ·
...It's an 04 TCCM which means it should be the updated one less inclinded to fail?...Lately my indicator lights on the switch sometimes do not illuminate at all? ...I also engage the selector to see if I could hear the actuator moving.....I could. ...
Only 2002 were really flaky and failed a lot. Your 03 is not as likely to die.

If your switch lights are out, but the functional test is fine, and your encoder motor AND front axle actuator are working and making noise when expected in each mode transition, then you may have just a bad light circuit.

When the lights go out, do you get expected mode transitions?

You could have a flaky PU/WH wire that drives the dimmable LED lights only. The big question is: Do the lights all flash at once when you turn the ignition on during the lamp test?

 
#102 ·
Thanks Roadie!

1. Functional test. Yes, all switch lights and gauge lights on at startup.
2. Encoder motor. I can hear it activating in the rear.
3. FA actuator. Not sure if I hear or feel it when lights are out.
4. Expected mode transitions. I am not sure it is engaging when the lights are out? The switch lights do blink between transitions and it does feel engaged when switch lights are on.

Hopefully I have given you enough information to advise if my TCCM "sleeps with the fishes?"
 
#103 ·
How often are the lights dark on you?

You say they are all on during the lamp test time, and then go dark later?

When they are dark, you can hear the transfer case encoder motor whine during mode transitions?

The FA actuator ONLY makes a noise (higher pitched) during 2HI->A4WD transitions and A4WD->2HI. You should be able to hear its noise superimposed on the encoder motor for those two transitions only.

When you say the switch lights blink during transitions, then I'm not clear on WHEN the lights go dark unexpectedly.
 
#104 ·
Good Morning Roadie!

I will attempt to give you more detail in my responses; why be slave to brevity? Especially when it leads to confused: Sorry I was way loose with jumping around on timeframes in my response.

How often are the lights dark? lately it seems to be about 30% of the time...but it could also be some observational bias as I have started to watch for the lack of lights now that I have seen it happening.

On during lamp test, and then go dark later? I need to observe this more...I will be sure to take note each time I start up and record what happens when I see the switch lights are out. I had not been noting it so closely prior to reading the posts after I noticed the condition. Everything was normal on the drive in this am.

When dark, is tc encoder motor whining? Yes...I believe that is the sound coming from the TC in the rear?

Is FA actuator engaging? It appears to be working when conditions are normal....I need to take better note when the abnormal condition reappears. I was unsure I heard/felt it last time I was trying to test in abnormal mode. I will use your 2HI to A4WD and back procedure next time I observe abnormal conditions.

When are lights going dark during transitions? Sorry...very poorly worded. I am unsure when it is they go dark....not sure if they did go thru lamp test as above. I was already underway when I first noticed the condition. I will be sure to do a better job of dx when in the abnormal condition as I am more carefully watching the lamp test now.

In the normal mode...the quick blinking between transitions was present if that helps. Then the switch lights were on as normal.

Thanks for all the insights Roadie! I will be sure to report back when more data is available. I appreciate your constant gentle pressure pushing me in the direction of a coherent response to your questions. I need that kind of editing!:)
 
#105 ·
... I appreciate your constant gentle pressure pushing me in the direction of a coherent response to your questions. I need that kind of editing!:)
THink of me as Dr. Gregory House, MD - but for systems, not people. In my day job, I'm often a diagnostician for million dollar semiconductor test systems. Not easy to get them to cough up their symptoms like a human can.

I even wrote this essay a few years ago in case anybody's interested in structured troubleshooting tactics.

http://www.roadie.org/bill carton's 16 rules .pdf
 
#106 ·
Nice Document!

Now that is one well thought out document!:hail: I wish I were more of a linear thinker sometimes. Needless to say I work in sales so my enthusiasm gets the best of me at times and I go short on detail!:yes:

Your timing is spot on. I just went to drive to lunch and meet my 22yo son and guess what?....cluster lights were normal....but no lights at all on the switch lights...either at startup or thereafter. I also did the 2Hi to A4WD test several times while moving at low speed thru the parking lot upon my return....I could neither hear nor feel anything? From either the front or back?

Should I order the 04 TCCM from the junkyard ($88 with ship)? From reading the posts I assume as long as it didn't come from a Bravada I am good? It says it came out of a TB. Or am I way off base?
 
#107 ·
Or pull out your voltmeter and check the voltages at the back of the switch and the TCCM. You should also pull off and reseat the connectors to eliminate common oxidation as a cause. You *do* have a meter, don't you?

TCCM could be a waste of $$. I'd look for a local trailvoy buddy to swap with first.
 
#108 ·
Volta what?

I was half expecting to see a sarc icon after the voltameter question!:laugh: I am pretty limited in both tools and talent. I dont have one...but I know they are fairly inexpensive for basic models.....I will buy one and google how to use it...and advise....it would be great if it were the switch as that appears to be the least pricey part at about $30.
 
#111 ·
4 wheel drive transfer case control module replacement

Roadie ,

Thanks for the help, even though I never asked directly.

This information you may find interesting..

I had a 2003 trailblazer with no-lights-on-knob, (only briefly when you first turn on the key). Also the same ;"Service 4 wheel drive" light turned on, on the dash. Yes, I said 2003.. I fixed by replacing the TCCM with a 2004. I wonder if they didn't put "leftovers" from 2002 in this truck.. The OLD/BAD unit's part number is 12580060.

This is the part number of the replacement TCCM that appears to work fine; "12588290".

Now...

I have 30 years of electronics experience and with one look at the "heat sink" (the aluminum piece with the fins on it), I could tell that it wasn't built heavy enough to run the transfer case shift motor. Besides this, when I took the box apart, I seen the worst sink-job that I have ever seen. The only way the controller ICs could sink ANY of the heat is THROUGH THE PC BOARD!!! (and through the paint and other coatings and a cardboard-like layer between the heat-sink and the PC board!)They may as well not bothered attaching a heat-sink at all. If they would have put the heat-sink on the OTHER SIDE on top of the ICs , it may have worked, but even then, the heat-sink that is there doesn't look like it would cool those chips while they are driving the shift motor at a 0 degrees when the motor and transfer case oil is very stiff. You might also think that hey, its cold out, it don't need as much heat sinking then, but this box is inside the passenger compartment next to heat ducts and worse, under the hottest part of a vehicle when the sun is shining..

I am sorry to say , but my 6 year old cold have come up with a better design!
 
#117 ·
#115 ·
2002 vs 2003 TCCM

I own a 2002 and 2003 Envoy. Had a bad TCCM in my 2002 and now have a messed up Transfer case disconnect on my 2003. Needed to get 4wd working for my wife or would be in the new car market. Good news is I was able to take the TCCM from the 2003 and put it into the 2002. Seems to be working fine.

Does anyone know if there is a need to get it flashed? Any issue with the two cars having different gear ratios?
 
#118 ·
Does anyone have an updated link to the pictures of the location of the TCCM and how to replace it?
Thanks
A lot of the content on this site has moved to another site. There is a dispute going on. This site changes the URL to point to TrailVoy and will not allow me to tell you where it is at. Might want to search for GM and then the word Nation with a dot and then the suffix COM.
I would go there and look. If no pictures, the guru's that posted it "live" on the site I suggested.
 
#120 ·
Check Elsewhere

I know this post is super old but does anyone still have these images? I'm in the process of trying to replace my TCCM. Thanks!
Did you read the previous post? Taking the inspection panel off the side of the dash was a MAJOR help to me in seeing the TCCM and getting it clipped back into place.

The forum GM t nation . com has a wealth of information and is the best group of guys on the Trailblazer. This is where the content got moved to.
 
#121 ·
There are a couple of threads about this issue, and Ive found this site very helpful. My 02 Trailblazer had no indicator lights on the 4wd switch and no service 4wd light on. I trusted my online research and bought a working tccm from a wrecked 03 Trailblazer on ebay for $80. I installed it myself and it worked like a charm. 4wd switch works great!! No programming necessary. The hardest part was holding the new one in place and simultaneously plugging the wires in with the limited access. Bloody knuckles on both hands, but they feel fantastic because 4wd is working as we get our first snow storm of the year in the Boston area. This website was a big help! Thank you!
 
#122 ·
TCCM bad

Thanks for the extensive T/S info. Roadie the schematic was priceless. You guys make owning this vehicle much easier.
No selector switch light. Blown fuse. reset connectors at TCCM replaced fuse. Blew another fuse (nbr 8) 30 amp. Replaced TCCM (got off EBay) also unsnapped fuse block shook down wiring suspecting possible chafing causing ground . Installed new fuse . Ops cks ok .
Oh yea I did remove the plug at xsfer case motor earlier before blowing another fuse so I decided the motor not to be cause . Next up change xfer case oil . Seen it mentioned enough to see the error of my ways.
 
#127 ·
help

Hello everyone i recently bought my wife a 2002 bravada with awd. it doesnt have a selector switch or anything just says awd. for some reason only the rear wheel spin, i changed out the encoder motor but that didnt fix it. i have no service awd lights or anything it just doesnt work. any help is much appreciated as we live in alaska and need the awd.
 
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