Hi folks,
been viewing for years, lost my username and re-signed up. i have a 99 blazer with the 4 button selector switch, and all the lights are on at the same time when running. I am no longer hearing the TCCM noise. in the past it would remain with all lights on while driving, apparently in limp mode. Then, I would hear the tccm noise and see an instant flash of the service 4wd light before all went out except the 2wd light. Problem lasted longer every cycle until now they stay on all the time. bypassing the vacuum acuator switch using metal tubing, the hubs do lock, but transfer case remains in 2wd. any ideas?

 

Check the connections at the TCCM, they like to corrode. If that's the case, clean them up and try it. If that doesn't take care of it, you can start throwing parts at it in hopes of finding the problem, or you can retrieve the body codes with a capable scan tool and post them here. The el cheapo scan tools at the auto parts stores can not access them.

 

hey thanks friend. I love this old 99Blazer, put some pics up, still in good shape. Bought it at 65k, now has 255k!! Anyway, I unplugged the battery for a few hours and after plugging back in, starting it all lights were on, then idling a few mins, I heard that telltale tccm noise, and only the correct 2wd light on. This morning, started it,all lights stayed on again for about ten mins, then back to 2wd light which is right. After an erand, started car again, once again all lights on, drove an hour and they never went out. Car is in 3rd and 4th gear only, unless i manually downshift. That means the encoder is good, tccm int? maybe the wire that plugs into the vac actuator on the firewall is bad? pins looked a bit moved around in there. any ideas? I will also scan at autozone if that works. Thanks again, I love 4 wheelin hard with this puppy!

 

i have a few friends that work at a dealership, they can maybe "borrow" a real good scan tool if thats whats need, thanks. i will try to clean the TCCM connections too, behind glove box? thanks.

 

TCCM is behind the passenger side kick panel.

 

Thanks! Me and an old mechanic friend took it apart, and sure enough the tccm was clicking as we wiggled the wires on it, clicking in to 2wd. We found corrosion on the harness plug, cleaned it up good and put it back together. It worked in the driveway, but now after turning it off and driving to work, it never clicked and returned to 2wd, all lights stuck on and in limp mode again, even after pulling to the side and wiggling all wires thouroughly. I can get a used tccm at the junkyard for $60, hopefully this fixes it, because we did get it down to the corroded terminl. Thanks for all the help in finding.

 

got the junkyard one, all is good now, thanks again.

 

Great! Thanks for posting back!