Hi, new member, I've searched and searched the net, various forums etc.

Here's our issue.... working on a 2000 Blazer for my neighbors daughter, has the 2 speed/automatic transfer case, it will go into "auto 4wd" but nothing else, when 4hi or 4lo is pushed the lights blink and then go back to 2wd. Fuses are good, grounds are good. I found some but not alot of corrosion at the TCCM connector and some at the seam of the TCCM itself, we cleaned the connectors and replaced the module, no change. When the auto4wd mode is active the vac solenoid on the firewall switches and I get 12v signal thru the front axle switch so the actuator and front axle are working properly. We checked the connectors at the encoder/shift motor and are getting 12v at the motor when 4hi or lo is commanded. Another motor was installed but again no change. I have checked the resistance on the front and rear prop shaft sensors and they are within range. I have the factory manual/wiring diagram so we've checked for high resistance in the circuits, so far everything looks good.

At this point I'm at a loss... what are we missing?

 

Same thing happened to my wife's GMC Jimmy, wound up being the slector switch on the dash board took care of the problem, hope this helps