Hello everyone. I've been a lurker for a while. Lots of great information in here.

I have a weird problem. 2000 Blazer with an NP8 4 button shift transfer case. My service 4wd light came on and all of the lights went out on my switch. There was a code posted, C0327 for the encoder circuit. Replaced the encoder, still had issues. Got another encoder again just in case I got a bad rebuild. I know the crap A1 Cardone puts out. Took it to a friend's shop, we went through everything and determined the TCCM was flaky. I got a rebuilt module and replaced it. Hooray, the 2hi button is lit.

When I hit 4hi, it goes into 4 auto. There was some corrosion on the large module connector. I ordered in new pins for the connector. I deponned the orange connector and have replaced the worst looking ones.

Right now the only way it will shift into 4hi is if I shut the engine off, turn the key switch to the on position, then hit the button. It may go in of there's enough vacuum in the reservoir to enable the actuator. Otherwise it will go on when I start it. It will not shift out while running. I have to shut the engine off then turn to on then it will shift back to 2hi. The same for the other ranges. The vacuum solenoid seems to be working, the actuator is working on the front diff. Rebuilt encoder, rebuilt TCCM. The switch was replaced also earlier this year, only because the lights were dim.

In a nutshell, it will not shift into 4wd while running, but will if it the key is on with the engine off.

Any thoughts?

Thanks!
Phil

 

Hey Phil. Reading through your symptoms, and the info you shared, I'd still suspect issues with corrosion at the TCCM harness, or possibly a bad ground for the same harness. I can't remember for sure, but I believe that the TCCM ground pack is nearby in the same area behind the passenger kick panel.

 

Thanks for the input. I'm thinking the same thing. I've been going through the harness and repinning the orange plug. The 4 pin wires and connector look fine. I'm tempted to patch in a ground wire and attach it right at where the module mounts. I verified the ground at the plug and while there's continuity, I don't know how good it is. I have not repinned that wire yet.

I worked on it yesterday. I pulled the fuses and reset the module. Everything was working while the engine was running. I could shift into all modes. I drove it for 20 miles and took it to an area where I could test the 4wd. No issues....

Then my daughter took it yesterday afternoon and said the service 4wd light came on. When she stopped where she was headed to, and restarted the Blazer, the light was off and and stayed off all the way home.

Thanks!
Phil