i have a 2001 Chevy blazer NP8 which has the 4 button selector switch. My issue is when I start the vehicle the lights on the switch all flash momentarily then remain off and the service 4wd light comes on after a few seconds. Also the actuator under the battery tray would engage the front diff each time the vehicle was started. Not sure if it’s tccm or encoder Motor. Thoughts?

 

The NP8 system codes can be read with an advanced code reader , thats where I would start. Now that system has a vacuum switch on the firewall by the distributor....If the front diff is locking when started I would bet that that switch is stuck open ...check if you have full time vacuum sucking through it. Can you hear the TCCM clicking at all ?, The encoder can normally be heard as well....the TCCM connections commonly corrode and cause issues , you could check and clean them.....I would start checking with some friends and see if someone could read the 4 wheel drive code or bring it to a shop that says they can.

 

The TCCM clicks right as the light comes on that says service 4wd, I checked and the vacuum switch isn’t stuck open but when I unplug the tccm the switch closes and the diff isn’t locked anymore, there is corrosion on the plug, what would you recommend for cleaning it, I’ve tried some electronic cleaner from autozone but it didn’t work to well at all. I’ll check and see if I can get these cleaned up some, I have a buddy that owns a shop that has whatever I need, I’ll see if he can squeeze me in for a few minutes, I imagine I should clean the plug before I go? Blazers are nothing new to me they’re all I’ve owned and I still haven’t taken one to a shop yet other than rebuilding a tranny that I pulled out, this has just got me stumped I have a feeling the corrosion is the issue but getting it cleaned is my difficulty as my “in” for the good cleaners got laid off from his job so they aren’t as readily available

 

tip cleaners for oxxy/acetylene torch tips seem to work good for the socket , you may have to be patient with a small screw driver and electrical cleaner for the pins....if the firewall switch isn't stuck...it must be getting permanent power for some reason. There is the GM diagnostic chart for this system on this site if you think it will help and you can't find it I can repost the info for you.

 

Good news problem solved! Ended up being the 6 prong plug on the encoder Motor was hit by a rock or something and was broken off, after that $180 encoder Motor all the problems are solved! Thanks for the help!

 

Nice , I keep an extra encoder on hand for my jimmy and astro....Just in case.