TCCM 2002 GMC 4WD Envoy 4.2

Buffalo1028

Original poster
Member
Dec 8, 2011
18
Hi,
I have not posted much, so if I am doing it wrong please let me know. I am having problems with my TCCM. I have replaced the switch on the dash, the 4WD Actuator motor under the passenger side, 2 tccms, both GM P/N 12590220. The TCCM's were both out of 2005 trailblazers. When I remove the fuse to disable the 4WD I now here the high pitched sound of what I believe is the 4wd Actuator. I do not hear the encoder motor when attempting to shift into 4W LOW. The guy I bought the last TCCM from said his mechanic told him not to use 4W Low. Mechanic said the clutches were worn and the motor traveled to far which than burned out the TCCM. Can that be correct? At this point I am about to pull the encoder motor to see if has any signs of life.

This forum solved my last problem with my throttle body. Thanks to everyone who helped me. I believe I had posted a thank you.

Any thoughts are appreciated. An encoder motor is about $155.00, I would almost rather buy one than go to the dealer. If the transfer case is worn, is repair or buying a transfer case from a salvage yard the way to go?

As always Thanks
 

Irishboy02

Member
Apr 1, 2012
222
4low will only engage on the truck while the vehicle is in neutral. It won't engage while in drive or park like 4high will. Find a flat spot, foot on brake, front tires straight and put it in neutral. Open your drivers door and hit the 4low. You should hear it engage, then you can slide it into Drive/3/2/1 whatever you want. Put it back into neutral and repeat the process to get it out of 4low. When coming out of 4low, I recommend to go from 4low to 4high, then 4high to 2wd. Not sure if its true, but the way the gears are set in the transfer case, I feel it is less stressful of a disengage if its done this way instead.

See if that works and let me know
 

McGMT

Member
Jun 17, 2012
621
When you remove the fuse and hear this noise, what do you have selected? 2HI? And why are u removing the fuse to disable the system?
 

Buffalo1028

Original poster
Member
Dec 8, 2011
18
McGMT said:
When you remove the fuse and hear this noise, what do you have selected? 2HI? And why are u removing the fuse to disable the system?

Yes i am trying to get back to 2 Wheel Hi. I remove the fuse to disable the system. It was shifting opn its own between 2wheel to 4Hi to reverse to neutral without rhym or reason.

Thanks
 

Buffalo1028

Original poster
Member
Dec 8, 2011
18
Irishboy02 said:
4low will only engage on the truck while the vehicle is in neutral. It won't engage while in drive or park like 4high will. Find a flat spot, foot on brake, front tires straight and put it in neutral. Open your drivers door and hit the 4low. You should hear it engage, then you can slide it into Drive/3/2/1 whatever you want. Put it back into neutral and repeat the process to get it out of 4low. When coming out of 4low, I recommend to go from 4low to 4high, then 4high to 2wd. Not sure if its true, but the way the gears are set in the transfer case, I feel it is less stressful of a disengage if its done this way instead.

See if that works and let me know

I can eventually get it back to 2 wheel hi. The truck shifts modes on its own with out any help from me unless I remove the fuse. I had replaced the TCCM Saturday when I posted. The truck ran great for five minutes, then the problems of shifting on its own occured.

Thanks
 

McGMT

Member
Jun 17, 2012
621
Buffalo1028 said:
Yes i am trying to get back to 2 Wheel Hi. I remove the fuse to disable the system. It was shifting opn its own between 2wheel to 4Hi to reverse to neutral without rhym or reason.

Thanks

That helps, now we have the issue.. Thanks.. Now, we gotta figure out why the control module is triggering. I am guessing that you know it is shifting on its own because the lights on the switch are telling you so. What you have to do is check the wiring going to the control module and the switch. Sounds like your switch may be goofy, might just have to spin it back and forth quickly to get the dust n stuff off the contacts.

One thing is, do you have a multimeter and know how to use it? You will need to check for specific voltages on the pins of the connector and such. If you don't have a manual for the vehicle they are available on this site. Before we go further let me know if you have the meter and are comfortable using it.
 

Buffalo1028

Original poster
Member
Dec 8, 2011
18
McGMT said:
That helps, now we have the issue.. Thanks.. Now, we gotta figure out why the control module is triggering. I am guessing that you know it is shifting on its own because the lights on the switch are telling you so. What you have to do is check the wiring going to the control module and the switch. Sounds like your switch may be goofy, might just have to spin it back and forth quickly to get the dust n stuff off the contacts.

One thing is, do you have a multimeter and know how to use it? You will need to check for specific voltages on the pins of the connector and such. If you don't have a manual for the vehicle they are available on this site. Before we go further let me know if you have the meter and are comfortable using it.

i,

The switch was replaced early on. I do have a multimeter. I am not real good with it. I can do basic tuff.

Thanks
 

McGMT

Member
Jun 17, 2012
621
Buffalo1028 said:
i,

The switch was replaced early on. I do have a multimeter. I am not real good with it. I can do basic tuff.

Thanks

Ok, then if you don't have a manual go here...
http://gmtnation.com/f23/need-service-manuals-get-them-here-371/

Get into the section for your year and the transfer case. In there you will see the wiring connector diagram for the control module, Check for battery positive voltage and a good ground and such.

Still with the replaced switch cycle it rapidly thru the modes (Key off) for a little bit to make sure the contacts are cleaned off.

Run your wiring looms to make sure you don't have chafed insulation letting thru stray voltage/signal anywhere.

If everything checks out alright, there is the possibility of the vehicle needing a new software calibration. Software driven systems like are all over these vehicles sometimes need a little help over time, especially if one goes bad and you replace it with another.

The t-cases use software to correctly engage the clutches and such so the encoder motor is open to movement whenever the system senses something in needs done or is not where it should be. Its all reaaaaly tricky. Check out the wiring and connections as mentioned above and let us know what you come up with. Even a small kink in a wire can cause a problem.
 

Buffalo1028

Original poster
Member
Dec 8, 2011
18
McGMT said:
Ok, then if you don't have a manual go here...
http://gmtnation.com/f23/need-service-manuals-get-them-here-371/

Get into the section for your year and the transfer case. In there you will see the wiring connector diagram for the control module, Check for battery positive voltage and a good ground and such.

Still with the replaced switch cycle it rapidly thru the modes (Key off) for a little bit to make sure the contacts are cleaned off.

Run your wiring looms to make sure you don't have chafed insulation letting thru stray voltage/signal anywhere.

If everything checks out alright, there is the possibility of the vehicle needing a new software calibration. Software driven systems like are all over these vehicles sometimes need a little help over time, especially if one goes bad and you replace it with another.

The t-cases use software to correctly engage the clutches and such so the encoder motor is open to movement whenever the system senses something in needs done or is not where it should be. Its all reaaaaly tricky. Check out the wiring and connections as mentioned above and let us know what you come up with. Even a small kink in a wire can cause a problem.

Thanks for the help and information.
 

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