Repairing a tranfer case control module

Way back in the 1970's when I worked at a shop that was authorized to work on GM products, a fellow from GM came around and was real proud that they were going from over one hundred shops in the country, to six, to two. That is what they have now is two that you are tied to through the new-car dealers' parts departments. There are independent shops that have sprung up that you can find by doing an internet search, but they do not get any support from GM. Most of those shops only handle common, easily-repaired problems, or they just send you a different module.

My preferred GM-authorized shop is United Radio of New York, in Syracuse. Be aware though they do not work on anything that has parts no longer available. They refused to repair a module for an 1988 model about eight years ago.

Also, be aware GM was the first manufacturer to dream up the need to program computer modules to the vehicle as a way to make more money. Their 2002 trucks were the first to do that, but it did not apply to every model that year, and not to every computer on the truck. If that applies to your truck and module, the people at United Radio should be able to pre-program a new one so you just have to plug it in and you are done.

Testing the module in the vehicle is possible but you need a Tech II or equivalent scan tool to cycle the module while watching the inputs and outputs. Testing out of the vehicle requires a specialized test bench that emulates the feedback of the T-case and front axle switch to the TCCM and PCM.

Those are the main reasons why they are expensive to procure.
I am going to assume you already checked the fuses and relays as well as removed and re-seated the connections on the switch and TCCM. The switch not lighting up is indicative of a loss of power/ground more than the TCCM. Those typically give you flashing lights or improper shifts not a dead system.

I have found a wiring diagram (below) and a guide to help you do some checks to see if the transfer case controller is getting power and ground. If all checks out I would get a used one and plug it in.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

and

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Here is the location of the module.

Please run this test and get back to us so we can keep helping you.

Cheers, Ken

Sure what do you need to know we can help you no problem.