Chevrolet Repair: 2002 trailblazer 4wd needs svc lite, controller area network, bells and whistles

Question
i own a 2002 trailblazer lt with all the bells and whistles. my 4wheel drive needs service lite came on . there are no faults shown with a regular scan tool. is there another service port to plug in to or do i need a controller area network scan tool? i can't find the info anywhere. i know 2003 and newer cars have "CAN" but there is no info on the 2002. i would appreciate any info you can provide.  thanks in advance  dave

Answer
Access to DTCs can simplify any system diagnosis. But these codes are not always 100% accurate.  Do you have any codes?  What are they?  Tech 2 is GM's official scan tool. It's always a good idea to make checking DTCs one of the first steps in your diagnosis.

GM has used many different four-wheeldrive control systems in its vehicles over the years, ranging from pure mechanical to electronically controlled. Each has its own diagnostic procedures, and the best source for understanding how these systems work will always be your information system.

The basic 4x4 system consists of a transfer case motor and encoder, Front differential actuator, transfer case module, speed sensors, switches and park input and output to the PCM.

GM has a problem with the dash switch.  Do you have a B2725 code?

Get the code and I can help from there.  

C J S