TCCM flaky when cold?

[Mooseman]

From reading other posts, I think that my TCCM is toast, or is it? When it is really cold (>-15C), the 4WD mode lights don't come on and the service 4WD light comes on. This happens when I first start it. After it has run a while and warmed up, restart it and it works fine and the service light stays off. 4WD will engage, no problem.

Any thoughts?

 

[The_Roadie]

Yep. Toast. Classic symptoms of a flaky 2002. At least you can order or locate a junkyard replacement without it being a huge emergency.

 

[Mooseman]

That's what I figured. Any difference between an '02 or were they improved in later years? I did see one of your posts that said that the '03 and later don't need to be programmed but if all I can find is an '02 that was already programmed, would that work?

 

[The_Roadie]

There was a hardware design fault in the 2002 units. Very high failure rate. Shun them.

2003+ units will all work, but if you buy a virgin one, it won't be programmed. Then you're into real money at the dealers who charge a minimum for their ten minutes of work with a Tech II.

2003+ used units will all work *IF* they've come from the same sort of system you have. A4WD/4LO systems on the Envoy and TB have different firmware than the AWD Bravadas. And I continue to forget which systems the Buick, Saab, and Isuzu have, but you almost never see them in the junkyard market anyway.

 

[Mooseman]

Excellent info. Thanks Roadie! I'll just have to troll the local u-pull yards for a suitable unit. Just hope that I won't need 4WD when it won't want to work

 

[zamimj222]

Guys, I have a 2004 with over 150,000 miles. My problem is that when my truck is cold, if I have it in AWD instead of 2WD or 4WD the infamous service 4WD light comes on the dash. After the truck is warmed up, it's of course fine again. Is it the TCCM and if so, can you direct me to the location of this little bugger.
Thanks!!!

 

[linneje]

Subject: Diagnostic Trouble Code (DTC) C0379 Set, Service 4WD Light On, 4WD Inoperative (Replace Front Axle Actuator) #04-04-19-001 - (02/23/2004)



Models: 2004 Chevrolet TrailBlazer, TrailBlazer EXT

2004 GMC Envoy, Envoy XL, Envoy XUV

with Autotrac Active Transfer Case (RPO NP8)




Condition
Some customers may comment that the Service 4WD light is on and/or the 4WD system will not engage. This condition may only occur after a cold temperature start-up (typically below -6°C to -1°C (20°F to 30°F).



The front drive axle actuator assembly engages the front axle in response to commands from the Transfer Case Control Module (TCCM). Normally, the cycle time for engagement is under 3 seconds, regardless of temperature. If the actuator does not engage the front axle assembly within 10 seconds, the TCCM sets DTC C0379, illuminates the "Service 4WD" light and disables the 4WD system. There have been reports of vehicles with front drive axle actuator assemblies that take longer than 10 seconds to engage, setting this code.

Correction
Important: When a vehicle with this concern is diagnosed in the repair facility, usually the inside temperature is warm enough that the system operates normally, and the C0379 will be set as a history code, making the concern intermittent and difficult to diagnose.

If following the diagnostic chart for C0379 does not reveal another cause for the code, and the temperature was below approximately -1°C (30°F) when the customer noticed the condition, replace the front drive axle actuator assembly with P/N 12471631.


The above might be a possibility. But the TCCM is under the dash about where driver's left leg is, if you were to replace that.

 

[zamimj222]

Subject: Diagnostic Trouble Code (DTC) C0379 Set, Service 4WD Light On, 4WD Inoperative (Replace Front Axle Actuator) #04-04-19-001 - (02/23/2004)



Models: 2004 Chevrolet TrailBlazer, TrailBlazer EXT

2004 GMC Envoy, Envoy XL, Envoy XUV

with Autotrac Active Transfer Case (RPO NP8)




Condition
Some customers may comment that the Service 4WD light is on and/or the 4WD system will not engage. This condition may only occur after a cold temperature start-up (typically below -6°C to -1°C (20°F to 30°F).



The front drive axle actuator assembly engages the front axle in response to commands from the Transfer Case Control Module (TCCM). Normally, the cycle time for engagement is under 3 seconds, regardless of temperature. If the actuator does not engage the front axle assembly within 10 seconds, the TCCM sets DTC C0379, illuminates the "Service 4WD" light and disables the 4WD system. There have been reports of vehicles with front drive axle actuator assemblies that take longer than 10 seconds to engage, setting this code.

Correction
Important: When a vehicle with this concern is diagnosed in the repair facility, usually the inside temperature is warm enough that the system operates normally, and the C0379 will be set as a history code, making the concern intermittent and difficult to diagnose.

If following the diagnostic chart for C0379 does not reveal another cause for the code, and the temperature was below approximately -1°C (30°F) when the customer noticed the condition, replace the front drive axle actuator assembly with P/N 12471631.


The above might be a possibility. But the TCCM is under the dash about where driver's left leg is, if you were to replace that.

This is probably a dumb question, but I am not that familiar with where everything is underneath my truck, where is this actuator located? Is this the motor on the side of the transfer case?

 

[The_Roadie]

The TCCM is a control module above the driver's left knee above the lower dash close-out panel. The encoder motor is bolted to the transfer case which is bolted to the back of the transmission. The front axle actuator (what is full of congealed grease and was the subject of the TSB) is on the front axle splined disconnect assembly on the passenger side of the oil pan where the CV shaft clicks into.

http://gmtnation.com/f79/repairing-front-axle-actuator-theory-operation-4612/

 

[zamimj222]

The TCCM is a control module above the driver's left knee above the lower dash close-out panel. The encoder motor is bolted to the transfer case which is bolted to the back of the transmission. The front axle actuator (what is full of congealed grease and was the subject of the TSB) is on the front axle splined disconnect assembly on the passenger side of the oil pan where the CV shaft clicks into.

http://gmtnation.com/f79/repairing-front-axle-actuator-theory-operation-4612/

I will look into the front actuator this weekend and see if it is indeed gunked up with grease and clean it up and see what that does for me. Thank you all for your wisdom and all the info you guys provide for the rest of us!!

 

[zamimj222]

I will look into the front actuator this weekend and see if it is indeed gunked up with grease and clean it up and see what that does for me. Thank you all for your wisdom and all the info you guys provide for the rest of us!!

OK, the update... I did not take the actuator all apart. I sprayed some degreaser into the plug in and let it sit for a few minutes. I then washed it out with some contact cleaner and cleaned the connector in the same way. I then before re installing the plug, I used some electrical grease in the pin end to make sure I had a good electrical connection. It seemed to work so far, I only drove it around the block a few times. I will check tomorrow on my way to work.