Service 4wd light

[haymakers23]

I was hoping to get some tips on how to fix my problem. I have a 2002 Chevrolet Trailblazer. I recently had a problem with it not running in two wheel drive. I scanned it and found that it had two codes. One for the encoder motor and one for the selector switch. After I was done replacing both of those, I went and tried to put the truck in 2HI all that would happen is it would just flash for a couple seconds and then go back into Auto. I brought it back to the dealer and since it wasnt throwing any codes they couldnt diagnose the problem. I went and bought a used transfer case control module and had it programmed hoping that would fix it. It didnt. That was all about 2 weeks ago. I was driving to work yesterday morning, when the service 4wd light on the dash came on. Before I take it to the dealer i was wondering if anyone here was had this problem or has any suggestions.

[navigator]

Hi Billy, I saw there were two threads so I deleted the duplicate thread.
Did you replace the selector switch with a new one or a used one? Sometimes they can get a little fouled up from not being used and if you cycle it a few hundred times it will help clean the fouling.

Most of the issues we hear of on here are the 4WD not engaging properly, there is a good write up on troubleshooting that at the following link.
http://www.offroadtb.com/articles/tech- ... wd-system/

It might be going through that write up might give you some tips until someone else chimes in.

[haymakers23]

Its a new selector switch but a used transfer case control module

[The Roadie]

Fire that incompetent dealer after you get your money back. Any competent mechanic with a high end scan tool can run a diagnosis without it throwing a code. A dealer especially with the GM Tech II tool can do it in ten minutes. The Tech II can bypass the TCCM and detect what mode the control switch is in, can command the front axle actuator to activate and deactivate, interrogate the front axle actuator's position feedback switch, command the transfer case encoder motor to go to any position, and also interrogate the encoder motor's position feedback potentiometer.

If any of these commands and sensors don't do what they're supposed to, then you have a diagnosis, assuming the tech knows the theory of operation of the 4WD system. If they don't know that, then they're incompetent to be touching your truck. Flee.

I have to assume you're running in 2HI mode most of the time. Running constantly in AUTO is one way to burn up the transfer case internals in under a year.

Please put the switch in 2HI, turn on the ignition, and describe exactly what's going on with your lights. What's the indication on the selector switch, and how long does it take to light up the Service 4WD lamp.

2002 had a HORRIBLE failure rate of the TCCMs. Are you sure your used replacement isn't from a 2002? What's the part number on your old and newer ones?