Intermittent 4WD

OldGuy96 · August 26, 2014

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 outof 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!

fondupot · August 26, 2014

you are shifting the trans into neutral when going in and out of 4LO yes?

OldGuy96 · August 26, 2014

Yes. I don't have an owners manual for the truck, but I figured you'd need to be in Neutral to go into 4 LO.

I'm suspecting the transfer case switch because I'm not getting any LEDs when I turn the ignition on, and the LEDs never light up when I press any of the selector buttons. I get nothing if I press a button.

OldGuy96 · September 3, 2014

I had a chance to do some diagnostics on the intermittent 4WD problem yesterday. I pulled the selector switch out and used a voltage probe to identify the power source in the harness. I then removed the front cover of the switch and plugged it back into the harness. When I touched the voltage probe to the power source terminal on the circuit board, the 2HI LED lit up. Playing with it a little more, I was able to select the 4HI and 4LO positions (accompanied by the appropriate LEDs lighting up. I was able to select 2HI again without any problem. In each case, the transfer case shifted to the appropriate gear, and the transfer case motor made no objection to accomplishing the shift.

I then put the front cover back on the switch and started to insert the switch back into the dash. At that point, the LEDs started flickering and then went out. I wiggled the harness around and the LEDs would come on and then go out as I moved the harness. Apparently, I have a poor connection within the harness.

Is this something that is common? Is there a good fix for this, other than replacing the harness and connector? Is there an inexpensive replacement for this connector? I found the best price for it on RockAuto, but it's still over $60.

gmtech4 · September 3, 2014

Bite the bullet friend and spend the money

OldGuy96 · September 8, 2014

I pulled the selector switch out and closely inspected the soldering on the contact pins. Several of the exhibited cold solder joints. A few minutes with my soldering iron, and the problem is corrected.