Intermittent 4WD
 

I have a '96 Silverado Z71, 350, 4L60, Push Button 4WD (NP1). The guy I bought it from was pulling a trailer out of a ditch and engaged 4WD LO, and then couldn't get it back in to 2WD Hi. Pulled the 3 button switch out of the dash, unplugged it, then plugged it back in. He got the LEDs to light, put it back in 2HI, and didn't think any more of it.

I was working on it and got it into 4WD LO, then couldn't get it to go back to 4WD HI or 2WD HI. Pulled the switch and plugged it back in. NOTHING. Disconnected the battery, let the PCM reset, then immediately tried to get it onto 2 HI and it went. The LEDs only flashed for a second when I changed modes and then they went out again. Since then, I haven't gotten any LEDs, but I'm afraid to mess with it much because I need to be able to drive the truck on paved roads, and being stuck in 4WD isn't a good option.

When the transfer case engages, it is almost instantaneous, which seems to say that there isn't any mechanical issue and the transfer case motor is good. Historically, what are the weak points in the electronics for the T-case? Is this Transfer Case Switch a common problem, or should I be looking deeper?

Thanks for any guidance!

After following some threads on other forums and a little help in replies on other forums, I finally tracked this down to being caused by poor solder joints on the 4WD selector switch.

I pulled the switch out of the dash and was able to get the LEDs to light up and the selector to work as long as I held the switch in one position. When I wiggled the harness, everything stopped working.

I pulled the switch apart and inspected it, where I found a couple of cold solder joints. I resoldered them, put the switch back together, reinstalled it it appears to be working properly now.

We appreciate you getting back and letting us know what you found. Those are the kind of problems you almost have to just get in and dig it out. Good job.

I would like to reiterate what SlimJim said
We appreciate you coming back to share your resolve with us.

I'm happy to be able to provide the updates.

I think that sharing the resolution to a problem is as important as sharing potential solutions to someone with questions or problems. If you don't share the solution, no one except you gains from your experience.