Hi all!

I have been working on my wife's Jimmy again (93, 4.3 W, NV233 transfer case). I bought it last summer and I've been working on it periodically over the past 15 months. Most recently I replaced the transmission. When I first purchased it in June 2010 the front axle was permanently engaged. I traced out the vacuum lines and the actuator was constantly engaged because vacuum was constantly applied. I replaced the switch on top of the transfer case and nothing changed. Eventually I gave up and just removed the vacuum hose from the actuator and capped it off.

Now that winter is near I've decided to dig back into the 4WD system. I pulled the TCCM codes and got a Code 2: encoder motor fault. I pulled the motor off the transfer case and it was corroded. I got a remanufactured unit from O'Reilly's and installed it and reconnected the vacuum line to the actuator.

We took it out for a test drive. That thing is a monster in the mud! My friend and I took it out for a run through the back 40 and had a blast! After the fun was over I got back to the serious part. With the 4WD switch off the truck is in 4HI. If I put it in neutral or park and press the 4HI switch the green light will flash and then it will shift from 4HI into 4LO. I can drive it around in 4LO and then put it in neutral or park and press the switch again and it will shift back to 4HI. If I press the 4LO switch nothing happens except the TCCM clicking. The yellow 4LO light never comes on, even when at start up during the bulb check.

Because the yellow light never comes on I'm suspicious of the switch. Is there a procedure for testing it? I'd really like to fix it tomorrow.

 

The switch on your truck is just contacts. No resistance or anything. There should be a line in for voltage and a line out for each of the buttons. When a button is pushed, the circuit between the line in and the corresponding line out should read continuous and less than 0.3 Ohms resistance. There will also be wiring for each of the lights. For the lights, you can apply voltage & ground to each of the proper terminals on the switch to illuminate the lights.

With the two button switches, pressing the switch for 4HI when in 4HI should switch back to 2HI. Same thing for the 4LO switch. Pressing the 4HI button when in 4HI should not result in 4LO.

Let me see if I can dig up a diagram for the system.

*EDIT* - Please find the wiring diagram attached to THIS POST.

 

possibly the led in the switch burnt

 

Thanks for posting the diagrams! I'll go through the switch in the morning.

Any ideas why it shifts from 4HI to 4LO when I press the 4HI button?

 

It is possible that there is some kind of wiring problem. I would testvthe wiring while you have the switch out as well.

 

I fixed it!

The switch was bad. The guy I bought it from in June 2010 told me that it had "some kind of 4WD problem; probably a blown fuse in the switch." When I took the left gauge cluster panel off I found the back side of it covered in some kind of hardened goop used to hold all the switches in place. My friend and I tested the switch and found it shorted out.

We went to the junk yard and found a '94 Blazer with the exact same switch setup. I bought it for $20. We took it home and installed it. The switch lit up as soon as I started it up to indicate it was in 4HI. I pushed the switch and it shifted out of 4HI perfectly. We took it for another run through the mud out behind the house and after a half hour of running through the mud (a good, thorough test) we determined that it was working properly.

So what was wrong with the previous switch? The previous owner had taken the 4WD switch apart and put it back together upside down. That's why when I would press the switch for 4HI it would shift from 4HI into 4LO. With the new switch and new encoder motor the system works perfectly. Thanks to all of you for your help, especially Kyle with his diagrams.

Now there's another issue with the Jimmy. I'll post a new thread for that.