4x4 - no communication

naui · January 19, 2006

I have a 2000 gmc sierra 2500 with electronic 4x4. Tried shifting from 2wd to 4wd one day and I received a message to service 4 wheel drive. I tried pushing the buttons a few times without any luck, I shifted into park and heard a loud grinding noise. I turned off the truck and while in park the truck rolled back. Restarted the truck and the 4x4 button lights flashed and all lights remained on, but I could not shift to two or four wheel drive. I tried disconnecting the battery for a minute then reconnecting it. This time no lights came on and there was no message to service four wheel drive. Had it towed to the garage, and was told that the actuator had to be replaced, this done and it still did not work. I was then told it could be the switches, I decided to bring it to the dealer for a scan to check the codes first.

The dealer could not get any codes, and suggested that the Transfer case control module would have to be replaced to get the codes. I was reading that the TCCM could be reprogrammed, but the dealer did not tell me this. Am I on the right track, replace the TCCM, and then the switches, or is there another way to pinpoint the problem without spending so much cash?

thanks

lou

GM-Tech · January 19, 2006

I'm not sure I'm clear on why they can get codes. Are they not able to communicate with the TCCM?

naui · January 19, 2006

I'm not sure I'm clear on why they can get codes. Are they not able to communicate with the TCCM?

<{POST_SNAPBACK}>

That's right, they were not able to.

GM-Tech · January 19, 2006

I'm not sure I'm clear on why they can get codes. Are they not able to communicate with the TCCM?

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That's right, they were not able to.

<{POST_SNAPBACK}>

I wonder if they tried pulling the fuse. Sometimes that will wake it up and allow communications.

Oh almost forgot to add... there are various calibration upgrades for the module, but to do them you need to be able to communicate with the module, so that's the first step.

naui · January 19, 2006

I'm not sure I'm clear on why they can get codes. Are they not able to communicate with the TCCM?

<{POST_SNAPBACK}>

That's right, they were not able to.

<{POST_SNAPBACK}>

I wonder if they tried pulling the fuse. Sometimes that will wake it up and allow communications.

Oh almost forgot to add... there are various calibration upgrades for the module, but to do them you need to be able to communicate with the module, so that's the first step.

<{POST_SNAPBACK}>

I don't think they tried pulling the fuse, the tech did not seem to have a lot of experience with these systems.

Does disconnecting the battery work the same as pulling the fuse?

And does the actuator have to be installed to communicate with the TCCM

GM-Tech · January 19, 2006

Disconnecting the battery would be just as good as pulling the fuse. No, the actuator doesn't have to be in place to program the TCCM.

naui · January 20, 2006

Thanks, I'll give the dealer a call tomorrow and find out

if they are up to the task of programming.

naui · January 20, 2006

I've tried disconnecting the battery for a few hours. I reconnected the battery and started the truck....still no lights on the 4x4 switches.

I did not plug in the actuator, should I have done this first before reconnecting the battery? Should the switches light up when started if the TCCM has recovered?

I have removed the actuator so that I can use the truck in 2wd mode.

Is there a way to test the actuator while off the truck to make sure it is working?

naui · January 23, 2006

I spoke to a dealer service advisor and was told that they could track down the problem at $96 per hour, but did not give me any idea of how they would do that.

I assume they would have special equipment to test each component, but did not

use them when I brought the truck in last week. Are there tools to test if the actuator is working and that the switches are working, or must the TCCM be operational first before anything else can be tested? And then it becomes a process of elimination?

Any help would be greatly appreciated.

Thanks

naui · January 27, 2006

Problem solved! Simple? you would think so. $500 later I find out that it is just a blown fuse! There are two fuses for the 4x4 system, one 15 amp. at the panel inside the truck labeled "4x4", and one 20 amp under the hood labeled "ATC" inside the main fuse box.