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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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#62 ·
TCCM Replacement

Thanks to your insite, I was able to read this post and fix the infamous "service 4wd" dashboard issue.

Same symptoms on an '02 trailblazer. no lights on the switch, fuse pull didn't work.

I found a used tccm mod at a junkyard for an '03 for $50 and replaced it with your pictures and instructions in less that 15 minutes!

Now to tackle the front right hub, to correct the ABS service light.

Thanks all!
 
#63 ·
access panel

I'm going through a TCCM swap on my '03 Trailblazer and after several attempts to unplug the TCCM connectors from underneath the dash, I noticed an access panel on the side of the dash. Open the panel and you have direct access to the TCCM connectors. Didn't see any mention of the access panel in previous posts so I thought I'd point it out.
 
#64 ·
tccm?

hi everyone,
i'm having similar issues with my 02 trailblazer LS. Noticed that i had no indicator lights on my 4wd switch one day and after checking this site tried pulling fuse #8. after replacing, the service 4wd light came on and i now have a solid awd indicator light and a flashing 2hi indicator light. vehicle remains in 2hi no matter where there switch is. i don't hear anything when moving the switch from one position to the next and the indicator lights remain as noted. considering replacing tccm but can't find a used one and wanted to hear what others thought before buying new and having programmed. Any thoughts?
 
#65 ·
I would call junkyards, after seeing who had a trailblazer by looking on car-parts.com. Your 2002 is most likely a bad TCCM, but it would cost you more than the used one would cost to go to the dealer and have then run a communications diagnostic. You have no local buddies with a similar vehicle to trade with?
 
#66 ·
checked that wedsite you recommended (thanks) and located a few yards in my area. Called a few of them and found a tccm from an 05 trailblazer. At first the guy i spoke to said he had a few of them in stock from 2002 - 2005 but he said i needed to check the id on the module itself to make sure one of these would match up. he proceded to give me several 4 digit numbers and told me to pull mine out and see if any of the numbers matched my current module. From what i've read, all of them are pretty much interchangable. Curious if anyone knows why he wants me to try to match the id # up.

And FYI for anyone who wants to know, $50 is what i'll be paying once i get this figured out
 
#67 ·
rpo lookup

I used this site http://www.gm-trucks.com/rpo-code-lookup/?find=gpu
I took a digital pic of the rpo sticker in the glove box and plugged in the 3 character abbreviations until I fould the one with my gearbox ratio. It started with the letter "G" I believe.

After that, I had the salvage yard confirm the rpo code on the vehicle they were taking the part out of to make sure the gear ratio was the same.
 
#68 ·
Service 4wd Light

I have an 02 Envoy and was having the issues with the lights on the selector switch not lighting up so I replaced the TCCM with one from an 03 Envoy from a junkyard for $75. After replacing the TCCM the lights on the selector switch now light up and I can switch between all the 4 wheel modes after first starting the vehicle.

Something still seems to be acting flaky though because if I keep it in anything other then 2 wheel drive the Service 4WD light comes on after awhile and the selector switch seems to stop responding. The light of the mode that it was in at the time the Service 4WD light came on does stay illuminated. Only way to get the selector switch to respond again seems to be to turn the car off and back on again. Any ideas?
 
#70 · (Edited)
So I've been reading about listening to the noises made when switching the 4WD selector switch. The comments seem to say to do this with the engine off and the ignition in the on position. The only time the lights on my selector switch light up and the only time noises are made when moving the selector switch is when the engine is running. From what I have been reading this does not seem to be normal behavior, is it?

Also, did a little more testing and it seems that the only time the Service 4WD light comes on and the switch stops responding is when I am in the A4WD mode. 2WD, 4HI, and 4LO seem to work fine. In the past I have noticed when in A4WD that the wheels bite when turning so it acts like it is not disengaging when it should. Maybe that is why it is throwing the Service 4WD light on and making the switch stop responding?

Guess the cheapest solution is to not use A4WD which I have read is recommended anyway.
 
#71 ·
Your behavior is not normal.

Did you change transfer case fluid at 50K as required? How is the level now? You might have encoder motor problems or grabby TC clutches to get full engagement in A4WD mode. Hard to tell without having the dealer command the encoder motor through its paces with a tech tool and see what's up.
 
#75 ·
TCCM location

Greetings, read through this entire thread. Is the tccm behind this panel in the picture? I couldn't see of feel it or see the loom of cables to it. In one post, they talk about an access panel on the side of the lower dash extension. I can see that this corner piece is a separate piece from the top of the dash assembly. Wasn't clear to me how to remove it. Wife wanted the car so I put the dash pieces back and will wait for another chance to find the tccm.
"The only that happens fast, is damage."
-Dave
 

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#78 ·
Greetings, read through this entire thread. Is the tccm behind this panel in the picture? I couldn't see of feel it or see the loom of cables to it. In one post, they talk about an access panel on the side of the lower dash extension. I can see that this corner piece is a separate piece from the top of the dash assembly. Wasn't clear to me how to remove it. Wife wanted the car so I put the dash pieces back and will wait for another chance to find the tccm.
"The only that happens fast, is damage."
-Dave

On the side of the dash you can see where a panel is cut out, just use a flat head screwdriver and you can pry it out. It makes it a lot easier to see the TCM and to know where your hand is at under the dash.
 
#81 ·
I had the same problem. My service 4wd light would come on. Took it to the dealer and they replaced the TCCM. Worked for about a month and now it is back on... The service 4wd light is on and no lights on the control. I have a 2004 XUV... It cost me $300 to get it replaced and now this. I have 200K on the truck. Just had the trans and engine replaced. It was cheaper to replace then fix. Dealership did it on the side for me. Any ideas why it would happen again?
Thanks
 
#82 ·
Start from the top

In short, no. Given my experience, I have bought a scanner and it is on its way so I can debug this rig without a trip to the shop. I would start by scanning to see what codes are set and go from there. Did you get a warrantee on the TCCM? If it failed, they should replace and reprogram the unit. http://forums.trailvoy.com/showthread.php?t=64219&page=4 post #31 from "the roadie" 'I still think it's the TCCM because a dead one won't light up any of the mode lamps. '
Do you hear anything when you move the switch to different positions? Some suggest 'exercising' the switch by rotating it all the way left and all the way right up to 100 times and see if that makes a difference. http://forums.trailvoy.com/showthread.php?t=68359 is a thread where you can see the insides of the switch.
Got a friend with a trailblazer/envoy that you can swap tccm's with? Easy to change and takes about 10 minutes after you do it once.
good luck!
-Dave
 
#84 ·
Huge thanks to Rhoadie and all those for the info. I just fixed this last night.

I had the Serv. 4wd light on for weeks. From the info on here with the newer part # I called my junkyard and had a newer 04 Envoy tccm mailed over for $75. Just popped off the knee panel, put my head on the floor looking up with a light from where the pedals are. You can see you simply squeeze the tabs on either end of the box, and it will pull out. Then you swap the clips over to the new one and pop it back in. It really takes all of 10-15 minutes, and I was in the cold at night. No more light, it all works awesome. Thanks fellas, hope others do this on their own and save money too. It is super easy.:thumbsup:
 
#85 ·
I too have fixed my tccm problem and O2 error codes (bought aftermarket.....first, ........acdelco to fix) thanks to everyones help (first post). Curious though, my tccm went shortly after I replaced my battery as well. coincidence? Someone else posted the same experience.:bonk:
 
#87 ·
Changed TCCM

i just changed out my old tccm with a new one. it was a little tricky but can be done by most people. i have a 2002 chev trail blazer ltz. my problem was that i could not engage my 4x4. the yellow light was not on for any of the four settings. eg. 4 hi 4 low ect. my tuck was a two wheel drive while the light was out and could not be changed. i took out the bottom pannel by the gas pettal and breaks. there was three bolts and some wires that needed to be taken off. than i removed the plastic pannel below the steering wheel. there where four bolts there. than i took a screw driver and removed the little pannel on the side of the dash that can only be seen with the driver door open. you must pry open the side closer to the driver top and bottom. once open you will be able to see the bottom of the tccm. there will be three wires going into it. i recommed to labble the two blue connectors for when the new tccm is installed. to remove the old you must lift up the tccm. there are two plastic clips that hold it on to the inside of the dash. the tccm is held there by a clamp. it may be a little tricky getting it out but harder to put back in. once you remove the old take the clamp off of it. attach that clamp to the new tccm. plug in the wires to the new tccm. now the trick part begins, you with have to play with it for a while to get it back to its original position. this took the longest of all the steps. once back in re atach all the pannels.

QUESTION - once the new tccm was installed there was still no light on the 4x4 switch. do i need to pull the fueses to get it out of sleeper mode? or is it when i get my TCCM programed by GM will the light reapear? thanks for the help

RECOMENDATION- i bought my tccm from shopgmparts.com i found there where the cheapest. i paid $ 180 US dollar for it. i also noticed alot of there other parts where cheaper than most sites and the ship internationally:woot:
 
#88 ·
QUESTION - once the new tccm was installed there was still no light on the 4x4 switch. do i need to pull the fueses to get it out of sleeper mode? or is it when i get my TCCM programed by GM will the light reapear? thanks for the help
If you got a virgin one from a GM supplier, you need to spend more money at a dealer to get it programmed. Sorry. They could have made them more plug and play, but no. Almost every other piece of consumer gear out here can be reflashed by plugging in a USB cable, but cars have to be made "special" because a mess-up (like the transfer case going into 4LO while on a freeway at 80 MPH) could kill people.
 
#91 ·
Great site, shopping TCCMs now. During Hurricane Irene, while contemplating running a 10-12" puddle, looked to the 4wd switch, noticed 'No Light' on the4WD selector switch, & backed out with a u turn.. Popped on here today finally, pulled Fuse 8, now switch illuminates during bulb check, then goes dark. 'Service 4WD' on dash now illuminated, it wasn't before.. Going to swap TCCM & report back.
 
#97 ·
Going to swap TCCM & report back.
In a bind for time, & couldn't find a used TCCM to try, so I took it to the Stealership for diagnosis, & estimate before repair.

2hr diagnosis/ install new TCCM, & flash TCCM, Drumroll please.... $612 + TAX!

Questioned how they knew for sure, service manager said it was definitively the TCCM, no codes for anything else, & will function perfect with new TCCM. Said 'No Thanks'! Paid 1hr labor for diagnosis, picked up and found a used '03 TCCM 45 mins away for $75. Ten minutes, and 4WD is fully functional again!

Thanks Trailvoy!
 
#92 ·
Good luck! My problem is I have a S4WD dash light, All the selector switch lights WORK JUST FINE but it won't shift. 2HI light id on solid, and when attempting to select any other mode, the 2HI light stays on, the new selected mode just blinks forever until I return it to 2HI, which stays on solid..WTF???? I hear the correct noises....
 
#93 ·
The noises might be there, but either the front axle actuator or the transfer case encoder motor isn't moving to the position the TCCM is commanding them to. A dealer or advanced independent mechanic with a suitable scan tool can talk to the TCCM and troubleshoot it precisely. Or you can take stuff off and shotgun it.
 
#94 · (Edited)
TCCM or.......

I just bought my used 2002 envoy at 270000km and it runs great except for 2 things. Bought as a second vehicle to tow :)
I noticed like many others that I do not have a light on my switch to indicate my drive mode. So reading up on the issue here and found a couple things. I first disconnected the battery for a while (40 min) Then pulled fuse 8 and 48 to try and get the TCCM out of "sleep mode" no luck. I then went to the junk yard and found a few of them to try before I purchased :) 1 was out of a TB 03 and the other a Enovy 04. Plugged em both in and still no lights on the switch when I turned the ignition on. At this point I was hoping for a SEL light to come on........but nothing. I'm out of cheep options to check.
Oh ya, prior to all of this I had gotten a saftey done and my mechanic did tell me that he did a diagnostic on the 4x4 and said the the switch was communicating to the tccm but the tccm wasn't communicating, hence the swap at the junk yard. He did pull some codes.....I'll see if i still have the paper and post.
If anyone has any ideas of what to check next please feel free :crazy:

The second issuse is the stalling at low idle.....i'll chime in the correct thread for that latter today once I clean out the tb (witch is new by previous owner) and look at the cpas?

EDIT: Any one know how much voltage is going though the number 8 fuse? I tested with the mult-meter and i read 0vdc. I also checked the voltage going though number 48 fuse witch gave me 13vdc. I don't have a schematic and not sure if any volts would be present on number 8 if the 4x4 isn't turned on or the tccm? I Also checked the connections to the tc motor and all looks good. Then again if i really do have a bad tccm and the 2 i tried at the junk yard were bad.....well my luck sucks then lol???
 
#95 ·
...Any one know how much voltage is going though the number 8 fuse? ...
Front fuse #8 (you didn't specify front or rear so I have to say front) is powered by constant battery power. It should be hot on both sides at all times. Rear fuse #48 is powered by the RUN mode bus only off the ignition switch.

You may have a TCCM communication wire fault, but the lack of ANY lights on the mode switch points to a lack of power or ground on the TCCM. I'd be checking the voltages on the various wires of the TCCM connectors.



 
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