My 4WD stopped engaging on my 1991 Chevy K1500 Pickup. I noticed the
4WD light was not coming on and I ran the truck up on the bottom of a
steep bank to check if it was not in 4WD or if it was just the 4WD
indicator light. Only the rear wheels were spinning and it definitely
was not in four wheel drive.
I had just used the 4WD a few days ago when I ran the front of the
truck up on ramps so that I could spray some rust inhibitor and
undercoating on it. The wax based rust inhibitor and waxed based black
undercoating were made by www.valugard.net and are approved by GM and
Chrysler. The rust inhibitor is a "cavity wax" that is sprayed inside
of doors and body panels but you can also spray it underneath the
vehicle if you want. It's supposed to be safe for electrical
connections but I guess I could have sprayed some on a connector and
caused a problem. I'm sure I did not get any of the actual black
undercoating on any electrical connectors, but perhaps I got some of
the cavity wax on the connectors. I had also blew everything off
underneath with some compressed air, but I did not notice any
connectors near the air nozzle. I'm not sure if something happened or
if it is just coincidence. I also greased the fitting on the front
drive shaft, but I don't see how that would contribute to a problem
After I backed the truck down off the ramps I parked it I left it in
4WD (I forgot I even had it in 4WD). Today I took the truck for a
short trip to the park and when I got there, I noticed that the
selector lever was in 4WD but the truck did not feel like it was in
4WD on my trip. When leaving the park, I move the selector to 2WD and
drove for a while and then moved it to 4WD so see if it would engage
and it would not go into 4WD. Neither the 2WD or the 4WD light show up
on the selector console on the floor.
The GM factory manual said to check the A/C-HTR fuse. I checked the A/
C-HTR fuse and it was fine. However, I had a 25 amp fuse labeled 4WD
and when I checked it, it was blown. I had a 15 amp fuse in a drawer
and I put that in just to see if it would get things working.
However, that fuse was blown almost immediately.
I was going to get some 25 amp fuses from NAPA tomorrow and see if
those fuses would work, but I suspect that those fuses will blow as
The manual says if it's not the fuse then it's the "transfer case
switch" or the transfer case linkage is disconnected or not adjusted
properly. The manual also says it could be a faulty transfer case or
front differential, but I'm guessing it's probably the switch,
provided the proper 25 amp fuse keeps blowing tomorrow.
How many switches are on the transfer case ? The manual says it's on
the left upper side of the transfer case. I think the 4WD indicator
light switch is a completely separate switch from the switch that
actually engages the 4WD. Can I check the switch with an Ohms meter
to verify if it is faulty or not ?
The transfer case housing is aluminum so I hope it's not a nightmare
getting the old switch out without stripping threads. The switch that
I saw looks very hard to get to.
If it's not the switch or a mechanical problem with the transfer case
or front differential, what else could it be ?
My only guess would be wiring or a rusted or faulty connection. I
seriously doubt it's a mechanical problem with the transfer case or
front differential, I've changed all the fluids at recommended
intervals, and have never had any noise or shifting problems with the
drive-train. There is about 100,000 miles on the truck now.
I would appreciate any feedback, advise, or similar experiences anyone