4WD problem

gui67

Original poster
Member
Apr 15, 2012
9
Hello,

I have a Problem with the 4WD on my trailblazer from 2002:
After having changed the front hub, I had the ABS light on: the connector from ABS had a bad connection. after having that corrected, there was no more light on the 4WD switch.
When turning the key on, the transfer case symbol does not light on the dash with all the other lights(ABS...)

I am now stuck in 2WD.

I checked the fuses they are OK (under the hood and under the rear seat).
I think I might have to change the TCCM, but what I don't understand is why the service light on the dash does not enlighten at all.

Last question: if I buy a used TCCM, is reprogrammation needed or is it plug and play? As i live in France, Chevy dealers are not so easy to find.

Thanks in advance for your help
Guillaume
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome, William! (same name as me)

Yes, the Service 4WD light should come on for a short time EVERY time you turn on the ignition, looks like this, in case you don't have your manual:

View attachment 20334

If it does not, then the lamp is simply dead.

When a 2002 TCCM dies, it fails to wake up when the power goes on. The PCM notices that there is no communication from the PCM and it's the PCM that turns on the "Service 4WD" light. A dead TCCM will also fail to light the switch lights at ignition-on time for their lamp test. So if the switch lights are also dark, I would look for a new TCCM, AFTER you confirm the TCCM has power. Even if the fuses are OK, there could be a wiring problem getting power to the TCCM. Do you have a voltmeter and want to look at the TCCM connector for power?

A new from the box TCCM will need a dealer to program it. A used one that has been in a 4WD (not an AWD vehicle like a Bravada) will already be programmed for you. See if you can find a friend with a trailblazer to trade with first.
 

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gui67

Original poster
Member
Apr 15, 2012
9
Thank you for your quick answer Bill.
OK, I will try to change the bulb from the sevice light.

Could you tell me on which pin from the connector I should look for 12V?

Trailblazer are not so easy to find here in France, I don't know anybody who owns one, but if there is no wiring problem, I will buy a used TCCM on Ebaymotors. It seems to be a common problem.

Will
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The TCCM gets its power on a 4-pin connector called C3. Pin A is black color - GROUND. Pin B is orange, 12V from underhood fuse #8.

The system will work OK even if the service light is dead. No need to change the lamp unless you're curious about the system.
 

gui67

Original poster
Member
Apr 15, 2012
9
the roadie said:
The TCCM gets its power on a 4-pin connector called C3. Pin A is black color - GROUND. Pin B is orange, 12V from underhood fuse #8.

The system will work OK even if the service light is dead. No need to change the lamp unless you're curious about the system.

I have 12V at the connector, so the module is dead.

Is there a way to us the transfer case without the module and without the motor, shifting manualy between 2hi, 4hi and 4lo:
there seems only to need one shaft to rotate. I have seen some kits for Ford trucks. I don't know if this is also possible for the trailblazer.
 

gui67

Original poster
Member
Apr 15, 2012
9
OK,
I have bought a used TCCM from a GMC Envoy.
I installed it.
Now the 4WD service light lightens on the dash when I put ignition (with the old one it did not lit when putting the key on ignition) but the switch light do not light.
The service light also lights when driving.
Is the switch dead? Or something other?

I opened it, there are only 8 LEDs and 2 small components, is it possible to find the default and repair it instead of buying a new one?
 

Sparky

Member
Dec 4, 2011
12,927
Do the lights on the switch at least momentarily all come on when you first turn on the ignition, or are they dark the entire time?

When my TCCM died in my 02 the service 4WD light didn't come on either until I attempted to reset the TCCM by pulling its fuse and putting it back. Then the service 4WD light came on. Kind of like what you have going on now... Makes me wonder if your replacement TCCM is defunct. What year Envoy did that TCCM come out of by the way?
 

gui67

Original poster
Member
Apr 15, 2012
9
The seller said he tested it and it worked.
The PN on the TCCM is the same, it is from a 04 Envoy.
The lights do not at all come on.
I checked the main connector on the TCCM, I have 12V on the Orange wire.

I will check the connector of the switch, with the diagram I found in an other post. and also the resistor values.

Guillaume
 

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