Ive read through multiple articles about 4wd not working, and haven't really came across my issue yet, so here is the rundown. I have a 00' ZR2. I was out wheeling last night and attempted to switch to 4 high. Not only would the button not work, but the truck decided to switch itself to 4 low instead. I couldn't put it back to 2 high, but I could switch to "auto 4wd". The 2 high and 4 high buttons do not work. I unplugged the battery and it went back to 2 high, but the same issue with the buttons is happening. I checked all the vacuum lines and hoses, and replaced a decent section of damaged line, with no change. What other issues could I be looking at?

 

Common problem is corrosion on the connector at the TCCM. If the corrosion is between the two pins that lead up to the dash switch, it can throw off the resistance of the circuit and cause it to switch mode/range at random. The Tech Article on the NV236 transfer case runs through this as well as the expected resistance values for the switch that can be easily tested with a DMM at the TCCM connection.

 

So I should check for corrosion at the tccm first?

 

Yes, and you can also check the resistance through the control switch at the TCCM when different buttons are pushed. This will require you to read and understand the schematics for those circuits.

Here is the link:

https://blazerforum.com/forum/tech-a...rmation-41198/

 

Just wondering if you ever found a solution. Mine is doing somewhat the about same thing. Started in 4wd low one day .. then it was stuck in 4 auto .. and had to reset TCCM to get it back into 2 hi. Hope it stays there long enough for me to find what's wrong. Pulled the TCCM and checked connectors. Checked vacuum actuator is holding vacuum and cable travel is good. Got fluid ordered -- hope it keeps working until it comes so I can change it -- sorely overdue for a fluid change...