TCCM Replacement How To

[Vartz04]

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
http://i7.photobucket.com/albums/y276/jefftheGRAFF/Trailblazer/TCCM005.jpg


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.
http://i7.photobucket.com/albums/y276/jefftheGRAFF/Trailblazer/TCCM001.jpg

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.

http://i7.photobucket.com/albums/y276/jefftheGRAFF/Trailblazer/TCCM002.jpg

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.

http://i7.photobucket.com/albums/y276/jefftheGRAFF/Trailblazer/TCCM003.jpg

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.

http://i7.photobucket.com/albums/y276/jefftheGRAFF/Trailblazer/TCCM004.jpg

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


any questions just ask here, don't PM me

[SweetD8943]

Great info - thank you so much for posting the process.

Any trouble driving the vehicle after swapping the TCCM out?

If you can - let us know what they get you for ($$) to do the re-programming of the TCCM at the dealership.

Thanks again - exactly what I needed to get this thing replaced on our TB.

Dave

[gordinho80]

TCCM needs to be reprogrammed? I had an issue with mine a few months back. I was getting the Service 4WD light and the switch didnt have any indicator lights on. I swapped out the TCCM with one from ebay, No Problems since... never went to dealer...

[SweetD8943]

Mario,

Someone, somewhere had mentioned that you do not need to get the newer, redesigned TCCM "reprogrammed" - whatever they did with the redesign eliminated the need to reprogram...not sure, but it sounds like it worked for you.

It will be interesting to see what they tell Vartz04 when he goes to the dealership...thanks for the input!

Dave

[480-Pelle]

TCCM needs to be reprogrammed? I had an issue with mine a few months back. I was getting the Service 4WD light and the switch didnt have any indicator lights on. I swapped out the TCCM with one from ebay, No Problems since... never went to dealer...

So did I, installed a -04 TCCM on my -02 TB...no problem. :thumbsup:

//Pelle

[Vartz04]

well I took mine to the dealer, they said they cannot communicate with the replacement. So something else is up I guess.

[SweetD8943]

Hey Jeff -

That sucks. Question: Did you ever get a trouble code reading for the TCCM to diagnose it? My mechanic originally ran the diagnostic and came up with a trouble code - it was # CO-550, which came up as something to do with the TCCM / ECU. Sort of vague though...

Just wondering if you were going off of a specific diagnostic trouble code, or off the hunch that it was your TCCM based on your research of the problem?

Thanks -

Dave

[TRAILBLAZER_GUY]

I know this Thread is over a month old, however i still think we need to follow up with the question asked previously, "Does another used 02 Trailblazer Module which is in current working condition a fix to install in an 02 Trailblazer with a bad TCCM?"


The Reason i ask is because i've heard that the 02 model TCCM is not Programmable... So does that mean that after the circuit is lost, it goes into sleep mode, Forever? Please share light on this since i find it difficult to understand that after a dead battery it would not work.

[ToddMeister]

I put a working TCCM from an 03 Trailblazer EXT into our 02 Trailblazer, works just fine, we did not reprogram the 03 unit. The old one out of the 02 was dead (no lights on 4WD switch/service 4wd light, dead TCCM code) I would think another working 02 TCCM would work in TB with a bad TCCM.

I know this Thread is over a month old, however i still think we need to follow up with the question asked previously, "Does another used 02 Trailblazer Module which is in current working condition a fix to install in an 02 Trailblazer with a bad TCCM?"


The Reason i ask is because i've heard that the 02 model TCCM is not Programmable... So does that mean that after the circuit is lost, it goes into sleep mode, Forever? Please share light on this since i find it difficult to understand that after a dead battery it would not work.

[booka96]

was wondering if the 03 and 02 tccm are interchangeable on the trailblazer. is the tccm located in the same place on the 03 as the 02. my 02 is on the drivers side and looking at another website it shows a picture of it on the passenger side http://kylestubbins.com/node/11 , they look different in the pictures. any help is appreciated

[the roadie]

They're interchangable, and located above the closeout panel near the driver's left knee. That other site you looked at was discussing a Canadian 2003 S10 full-size Blazer. Not a GMT360 trailvoy kind of vehicle.

[booka96]

thanks for your reply to my question, i am trying to decide which avenue to go with. i found one in a junkyard in an 03 for $75. i hear the dealer charges $275 for the part alone and that it still has to be programmed. is this true? or can i just install a new one and avoid the dealer? or can i just put in a used one and be done without having to program?
thanks for your help, i would love to avoid the stealer i mean dealer.

[YukonLTZ]

I have a similar problem. Every now and then my 02's battery would be dead. I could not for the life of me figure out why. It would be fine for a week, a month, a day. Even fully charged it would sometimes be dead 2 hrs after the lalst time I ran it. After each dead battery the lights on the 4wd selector were out and I could not change out of 2wd. After driving for a random amount of time it would come back on and be fine til the battery died again. I broke down and took her to the dealer. They said the ignition switch was draining the battery. They changed it out..275. They checked the tccm and it is dead. The truck is going back in next week when the part gets here. GM tccm in Whitehorse Yukon?.....675$ plus labour. Guess I have to do my part to keep them out of chapter 11. After hitting this site. Im feeling a bit ill knowing I could have fixed it myself. Id tell them to go pound sand, but I already agreed to have them ship one here and have them install. Next time something is wrong Ill check TRAILVOY first. Great site people. Keep it up puleese!

[the roadie]

...or can i just put in a used one and be done without having to program?...Sorry for the late reply. The TCCM should have the VIN programmed into it by a dealer's tech tool so it knows what gear ratio is in the vehicle. It also needs to know if it's being put into an AWD or 4WD vehicle - same TCCM is in both of them, but only the 4WD TCCM needs to control the front axle actuator. AWD vehicle's front axles are engaged all the time mechanically, and are missing the splined disconnect and actuator installed in the part-time 4WD trucks.

Many members have bought used TCCMs and plugged them in and they work fine, because statistically (I think) most of the vehicles with control problems are 4WD and even if the gear ratio is off the functional effect is minor.

... took her to the dealer. They said the ignition switch was draining the battery. They changed it out..275. Down here, you can buy a switch for US$30 and change it in a half hour. But you found that out already, I expect.They checked the tccm and it is dead. The truck is going back in next week when the part gets here. GM tccm in Whitehorse Yukon?.....675$ plus labour. $200 at parts4chevys.com. $75 on Ebay. 15 minutes to install. Then you pay the dealer 1/2-1 hour to program.Guess I have to do my part to keep them out of chapter 11. The mechanics have to eat, too. And by paying the local dealer, you keep them from begging in the streets. At least the money isn't going offshore or to Mexico. :ugh:After hitting this site. Im feeling a bit ill knowing I could have fixed it myself. Id tell them to go pound sand, but I already agreed to have them ship one here and have them install. Next time something is wrong Ill check TRAILVOY first. Great site people. Keep it up puleese!Thanks. We try. :D

[YukonLTZ]

Hehe, true enough. Maybe I can help wake someone up who is on the "job bank" program and get them out of the lunchroom.

[booka96]

Thank you for your replies, they are very informative and greatly appreciated. due to my frugalness, i think that i will be trying the salvage yard route and gamble with the $75 that he wants for the part. when i ever get around to it i will let you know of my outcome, since the snow has left us for the season now. i did however take the old one out to get the numbers off of it and when i reinstalled the tccm, the trailblazer did not want to start. it sounded like the timing was wayyyyy off, it finally started and worked its bugs out though, i guess some of the computer info was out of whack.

[Hid-hq]

ok so which hARNESS ties in from the the 4wd switch to the tccm?

Working on an olds bravada 4wd swap.....I have essentially all the mechanical parts tccm 4wd switch harness etc.....

I know the tccm between the bravada and tb are the same p/n....

So thaT means that the wiring/pinout are similar if not the same,,,,,,

So can I splice into the bravada harness. and run it to the 4wd switch?

[the roadie]

The TCCM has more features than the Bravada harness can support. Specifically, the Bravada doesn't have the front axle actuator, and its TC connector is 5-pin (no brake solenoid) versus the TB's 7-pin. But many of the connectors are the same, such as the ones on the switch and TCCM.

[melonhead]

The directions on this post are great on how to install the TCCM. However, the photos have been removed. Is there anyway you can repost them or I can retrieve?

Thanks!

[the roadie]

Only if he gets them rehosted. I don't trust free picture hosting, and recommend people attach pics to their threads to make sure trailvoy hosts them here for longevity.

Anyway, here's a compnine.com exploded view of the location. The TCCM is item #2. It's really quite trivial once you know about where it is on the dash panel above the driver's left knee.

http://www.compnine.com/largeimg/010302TS04-034.gif

[melonhead]

Thank you so much! This will help immensely!

[atandt3k]

The picture you have for the link is for a Chevy s10 Blazer, not the Trailblazer.:thumbsup:

[the roadie]

... for a Chevy s10 Blazer,......as I pointed out in post #11. ;) Good eyes, though. There were some confusing years when they produced Trailblazer trim level Blazers (and an Envoy) on a non-GMT360 platform.

[cadyshac]

My '02 trailblazer is experiencing this tccm problem. I did have to replace my battery and that is when the 4wd started acting up. No lights on the selector switch and no switching out of 2wd. I don't understand what the Roadie was talking about a couple of posts back about full time AWD versus 4wd vechicles. I can go from 2wd, 4hi, 4lo, and Awd and I thought all of the TB's were like this. I would like to get a junkyard tccm so if I find a vechicle with the same selector switch as mine will the tccm from it work? I have tried pulling fuse 8 but I don't know if I had it out for a full 30 seconds or not, I will try this again first.

[cadyshac]

I may have answered my question, I am confusing A4WD (automatic) with full time all wheel drive. Basically if I get another tccm out of a junkyard will it work on my '02 TB? Does it have to be out of a TB or can it be an Envoy?

[FunkZ]

In my 02 TB the part I pulled out of mine is 15085386 and the one I put in is the 12584313 from an Envoy.

AFAIK all of the platforms are compatible including TB, Envoy, Rainier, Bravada, Ascender. I believe that the important thing to match up when buying used is the gear ratio, which is standard 3.42 but others were optional such as 3.73 or 4.10 ratios. Or you can have it reprogrammed.

[the roadie]

AFAIK all of the platforms are compatible including TB, Envoy, Rainier, Bravada, Ascender. Some of those models are only available in AWD. Others in true 4WD with a LO range transfer case. But you're right, they all use the same TCCM - it's programmed by the factory or the dealer as to which kind of vehicle it's controlling.I believe that the important thing to match up when buying used is the gear ratio, which is standard 3.42 but others were optional such as 3.73 or 4.10 ratios. Absolutely critical. But many junkyards have NO IDEA what gear ratio vehicle they've stripped parts off of. :thumbsup:Or you can have it reprogrammed.If you mean the TCCM, that's right. But sometimes dealers charge more for this than just buying the right one used in the first place. If you mean the differentials, regearing their ring and pinion will most likely cost more than buying the right one used in the first place.

[cadyshac]

I found a "you pull the part" salvage yard that only wants $30 bucks for a tccm. Is there somewhere on the vechicle that I can identify what rear gear it has so I can compare it to mine? What if I get one from a vechicle with a different gear ratio? I dont use 4wd very often but do use A4wd frequently in the winter months.

[the roadie]

Is there somewhere on the vechicle that I can identify what rear gear it has...Glove box RPO code sticker.

[cadyshac]

Thanks for the info, I will check my code. What if I cant find a junkyard part that matches my gear ratio? What will happen if I use a tccm programed for a different ratio? My truck has 190,000 on it and I really dont want to pay the dealer to reprogram the tccm. For any of you wondering my truck looks like it has 50,000 on it the leather interior is like new and it runs like a top. I am the original owner and have taken good care of it.

[the roadie]

I think the worst that can happen is that the algorithms are slightly off for ground speed in the A4WD mode. No sweat, because that is almost a totally worthless mode anyway. The engagement is potentially abrupt, and if you're not slipping it won't be engaged anyway. If you're on a slippery surface, you should be in 4HI. I wouldn't worry about the gear ratio. Just don't buy a flaky 2002 model.

I don't understand why so many folks see a benefit in the A4WD mode.

[Vartz04]

http://i7.photobucket.com/albums/y276/jefftheGRAFF/2002%20Trailblazer/TCCM005.jpg

http://i7.photobucket.com/albums/y276/jefftheGRAFF/2002%20Trailblazer/TCCM004.jpg

http://i7.photobucket.com/albums/y276/jefftheGRAFF/2002%20Trailblazer/TCCM003.jpg

http://i7.photobucket.com/albums/y276/jefftheGRAFF/2002%20Trailblazer/TCCM001.jpg

http://i7.photobucket.com/albums/y276/jefftheGRAFF/2002%20Trailblazer/TCCM002.jpg

i thought I pmed these to roadie a while back, feel free to put them back in the original thread.

[fredmertz]

First, I'd like to thank everyone in this thread for your sage advice.

Before buying a new TCCM (2002 TB LTZ with service light on and no indicator lights), I took off the panels to gauge how easy it would be to swap out the module.

I'm a bit of a newbie at doing things myself -- but I have successfully replaced the factory stereo with a bluetooth/satellite radio unit.

So here's my issue -- I had no problem getting the two panels off, but I could not figure out how to get the panel/plate underneath them off without taking off the entire dash. Is that what I need to do? I am hoping to avoid that. is the difficulty with the installation that you can't get it off?

Thanks!

[cadyshac]

I cant see what you have removed but if you have removed two panels you should be able to access the tccm. Are you sure you need to remove something else? You definitely dont have to remove the entire dash. After locating the tccm in my vechicle it only took a couple of minutes to disassemble and remove the unit from the junk car I got mine from. Use a good light and make sure you aren't overlooking something.

[fredmertz]

When I take off the two "external" panels there is a hard plastic panel where the driver's left knee would be. I believe I can make out the tccm behind this panel, but it seems to be very difficult to access it without taking that panel off.

Should I be able to see the tccm clearly just by removing those two panels?

Thanks

[cadyshac]

From what I can remember I didn't take anything more than the two panels that Vartz shows in his pictures. It may be a little hard to see the tccm but look around I dont remember anything else close to it with three wire harnesses connected to it.

[gregl01]

Yeah, I wondered the same thing. You have to reach your arm up from behind to get to the tccm. The pictures don't clearly show where its located and how to access it. Easy to fix once you get it pulled down though.

Greg

[Vartz04]

its back up in there you have to be a kind of contorsionist to get in there and pull it out, its held on by a clip and you can unplug the harness and pop it out.

[Nozzleman]

So I don't have any codes stored. Except for the SVC4WD light, all seems to work except it won't go into 4WDLO. Is that the typical failure mode for the TCCM or do I look for something else? On initial start up the lamp is out until I hit 15MPH. It was in 2WD when the lamp came on. The lack of a code puzzles me.

[the roadie]

.. it won't go into 4WDLO. ...Are you in neutral and coasting less than 5 MPH when you try to go into or out of 4LO? There's an interlock.

[Nozzleman]

Sitting still, <5MPH in neutral, doesn't make any difference. The indicator flashes an unusually long time and reverts to 4WH.
Should I get a code at the customary port or only on the TCCM?

I'll say that I have only had this vehicle for about a month, so I am still learning its habits. It has less than 60K miles. I've already gone through the gauge motor thing. Bad omens, huh?

[the roadie]

The error code will only be on the TCCM, if you have a scan tool that can talk to it.

Did the previous owner change the transfer case fluid at 50K miles? Have you checked its level? The encoder motor is the biggest thing needed to change to 4LO, but if the transfer case hangs up mechanically, it will jam the encoder motor and explain your symptoms. Getting to a dealer or mechanic with a high end scan tool that can command the encoder motor through its entire range of motion is the thing I'd do next.

[Nozzleman]

Bought from a GM dealer who changed the engine oil but I don't know about the TC oil.
I did the Autozone free scan but it apparently wasn't sophisticated enough to read the TCCM. I have 2 reputable shops that can read it for me but probably not for free. I'll spring for the $$.
I have to believe that it's electrical as 4WLO worked soon after I bought it for a brief test. I wasn't in 4wd mode when the service light came on. In fact, it was off the night before and came on soon after leaving my driveway in the morning. The scan will tell.
Thanks for the ideas.

[Nozzleman]

New info. At initial turn on, the SVC4wd lamp is off. 4wdLO engages. Drive to 15-20MPH and the lamp comes on. It will not switch out of 4wdLO. Turn vehicle off then back on, the lamp is off. It now switches out of 4WDLO to what is selected. It's as if it is not receiving a speed pulse and the SVC4wd lamp locks up the selector.
Shaft speed sensor??

[the roadie]

I think you're right. Never saw a report like that here in my time on the forum. See what the TCCM scan reveals.

[Nozzleman]

I'll report after the scan.
Thanks for the guidance.

[dbelcher]

I have a 2002 GMW Envoy. My 4x4 service light was on and the dash switch had no lights (other than when the vehicle first started).

I decided to pay for the dealer to troubleshoot (about $100). It was the TCCM. I had read on various posts that the 2002 model year had issues with this part. I went to the local wrecking yard today and pulled one from a 2003 Trailblazer ($50). I changed it out tonight. Mine unit was located just as others had noted...under the dash panel on the driver's side. It took me about 25 minutes to remove the panel, get my hand up to get into a position to unplug it, and reinstall the new unit and dash panel. I did not disconnect the battery. When I restarted the vehicle the service 4x4 light was off and the light 2 wheel drive light on the switch was illuminated. I did a test drive and sure enough it was switching back in and out of 4 wheel drive. Overall easy repair. I probably could have saved the $100 dealer charge for the diagnosis, but I was a bit more conservative.

[the roadie]

Thanks for the report. 2002 TCCMs really bite. Dumb GM design team.

[fredmertz]

So I replaced the TCCM and the service 4WD light is not off, but the 4WD indicator lights no longer turn on when the car starts and there is no indicator light. This was the original problem that led me to pulling the fuse -- it was only after I pulled the fuse that the service 4WD light turned on.

Any ideas?

[the roadie]

Where did you obtain the TCCM you put in? Was it a known working used one? Sounds like a bad 2002 unit that won't wake up at ignition on time.

[fredmertz]

Where did you obtain the TCCM you put in? Was it a known working used one? Sounds like a bad 2002 unit that won't wake up at ignition on time.

Bought it brand new from gmpartsdirect.com, so I assume it is new and of recent vintage.

[the roadie]

Bought it brand new from gmpartsdirect.com, so I assume it is new and of recent vintage.Oh, sigh.......you must not have read my advicethreads like these with the proper eye for details. If you got a used one from Ebay or a recycler, it would have been programmed and ready to roll. Now you have to go to a dealer who will load the right configuration software into the module's memory to make it work. It's like buying a PC with a clean hard drive, but no Windows disk to load it up. Some dealers charge a fair price for ten minutes work - some charge a rip-off one hour minimum. Good luck.

[fredmertz]

Oh, sigh.......you must not have read my advicethreads like these with the proper eye for details. If you got a used one from Ebay or a recycler, it would have been programmed and ready to roll. Now you have to go to a dealer who will load the right configuration software into the module's memory to make it work. It's like buying a PC with a clean hard drive, but no Windows disk to load it up. Some dealers charge a fair price for ten minutes work - some charge a rip-off one hour minimum. Good luck.

Even worse -- I read everything with a fine tooth comb -- just completely MISREAD it. I thought that 'programming" was optional, but now I see that it is "exact programming for your particular car model/trim" that is optional.

Thanks for your help -- even if I have to pay an hour worth of work for the programming, I still saved at least $300 on not paying for a diagnostic, an hour of labor (for a 5 minute job) and overpaying a dealer directly for the part.

All in, this thread has been a godsend!

[Nozzleman]

Finally got my issue solved. C0300 and CO305.
Rodents ate the wiring of the main harness at the TC. Seven chewed on, two chewed through. Seems to be a convenient perch to sit and nibble there. Luckily none shorted. The copper was quite oxidized and appears to be from the previous owner. I can hope, anyway. Replaced all of the wires and a new connector. Rewrapped the loom and put convoluted tubing over it.

I picked up an 05 TCCM just in case. It came from a std 3.42 geared vehicle. Mine's 3.73. Does it need to be reprogrammed if I ever use it?

[the roadie]

That's certainly a first rodent report here. Thanks for coming back and telling us what happened.

The TCCM needs to know the vehicle's gear ratio for only a couple of minor reasons. To make sure the 4LO inhibit speed it close to 5MPH ground speed, since all it knows about is driveshaft rotation speeds. This is not very important, since most folks do it while stopped anyway. The other is to optimize the algorithms used for clutch engagement under A4WD conditions. Who cares?

Personally, I advise against A4WD operation for safety's sake and the lifetime of the transfer case. The way A4WD works is to wait for front/back wheel slippage, THEN tell the encoder motor to engage the TC clutch plates to reduce the slippage. Sometimes they engage with a jolt, which can BREAK LOOSE tires that were only slipping slightly, and aggravate a skid in progress. The sudden engagement has also been linked to breaking an underdesigned clutch pressure plate bearing.

If it's slippery enough to need 4WD, then just go into 4HI. If it's not slippery enough, use 2HI and deal with the predictable and unchanging driveline performance. Offroaders with upsized tires (from 29" stock to 33-35") have effective gear ratios much lower than the one programmed into the TCCM, and AFAIK, aren't seeing any adverse effects.

Discussed in TSB #08-04-21-001B

[lloydx6]

After reading threads about the TCCM I am still unsure if that is my problem. My selector switch does not display any lights, only drives in 2hi no matter what the switch says and does not throw any trouble codes. What is the final consensus on used and new TCCM's? Are the new ones preprogrammed, are used ones plug and play? I am going to start somewhere, I just want to make sure I am making the best choice. Thanks.

[cadyshac]

The used ones are ready to go just plug it in. Call around and see how cheap you can get a used one for. Just don't get one out of another '02. My '02 was doing the same thing as you are describing and I put in a tccm from an '03 for $10 (bargain of the century). Works like new.

[the roadie]

It can cost you more than $100 to have a dealer give you a FIRM diagnosis (and even then no guarantee) that it's the TCCM. And you can put in a junkyard one for less than that. Just make sure it's not a fuse (#8 under the hood) causing the lights to not come on.

If you need a free way to confirm you're making the best choice, then you have to find a local trailvoy 4WD owner to swap TCCMs with.

New ones you buy from a dealer or Internet GM parts vendors will NOT come programmed, and you have to show up at the dealer, again with +/- $100 in hand, and have them do their 10 minutes worth of magic.

For reference: GM #12590220 - $200 at parts4chevys.com, $273 list price.

[Vonhendon]

I have an 02 Voy and sometimes mine will flash for awhile and then go to neutral,or it will be in 2hi and just not switch when I need it to. This happens mostly when it's real cold and windy. Guess i need one of them TCCM 's

[the roadie]

Your problem could still be the switch. You could try turning it end to end 100 times or so with the power off, and see if it gets better. Or replace it first, since it's cheaper. But if you get a junkyard opportunity, pick them both up if you can, and make sure it's from 2003 or later for best reliability.

[Vonhendon]

Thanks Roadie I was hoping to get your advice. Your knowledge on these board's is PRICELESS

[eggman]

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!

[NigelTufnel]

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.

[wholeman11]

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?

[the roadie]

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?

[wholeman11]

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

[eggman]

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.

[envoy02owner]

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?

[the roadie]

Either your front axle actuator or the encoder motor is slow to act, or dead. Search for other threads on the subject of identifying which one it is by sound.

[envoy02owner]

Either your front axle actuator or the encoder motor is slow to act, or dead. Search for other threads on the subject of identifying which one it is by sound.

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.

[the roadie]

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.

[envoy02owner]

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.


I have not had the transfer case fluid changed so I will get that done and see what happens after that. Thanks for the information.

[envoy02owner]

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.

Hey Roadie a little more information for my selector switch lights not coming on with the ignition in the Run position. It appears there are other electric components that are not coming on as well. I noticed the Radio, odometer display, 4WD selector lights, and all of the gauges (they don't move at all) remain off with the ignition in the Run position. If you start the vehicle all of these components come to life and work fine. With the ignition in the run position I do get the Service vehicle Soon light and the parking break light on the dash to come on and all interior and exterior lights come on. Any idea on what is going on there?

[the roadie]

Start with the ignition switch, then. Usually $28 at any aftermarket store. High failure rate item blamed on all sorts of flaky electrical issues.

http://forums.trailvoy.com/showthread.php?t=61278

[cntinuum]

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

[fredmertz]

You need to reach up and around the bottom of that big panel. You won't see it, but you can pull out the unit and it will hang down on its cables.

[cntinuum]

Thanks, will give it a go

[envoy02owner]

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.

[FunkZ]

It looks like the original pictures were moved or a folder renamed:

http://media.photobucket.com/image/tccm%20trailblazer/jefftheGRAFF/2002%20Trailblazer/TCCM001.jpg
http://media.photobucket.com/image/tccm%20trailblazer/jefftheGRAFF/2002%20Trailblazer/TCCM002.jpg
http://media.photobucket.com/image/tccm%20trailblazer/jefftheGRAFF/2002%20Trailblazer/TCCM003.jpg
http://media.photobucket.com/image/tccm%20trailblazer/jefftheGRAFF/2002%20Trailblazer/TCCM004.jpg
http://media.photobucket.com/image/tccm%20trailblazer/jefftheGRAFF/2002%20Trailblazer/TCCM005.jpg

[cntinuum]

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. I don't think I could have got the tccm back into place w/o the access panel being open. It was a pita to get the holder to snap back in the slots. The visibility through the access panel was very helpful. In the picture, you can see the tccm plugs, barely and the black clips on the bracket coming thru the aluminum mount.

[FplcMan]

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

[cntinuum]

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?
ThanksIn 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

[FplcMan]

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


Going to the Dealership on Friday. I was not using it. It just comes on when it wants to. When the light is off I did change the positions and it made the correct sounds. I will post back what the dealership says. They better not charge me that $100 fee to test it.