4WD not working - Help!

[code.mafia]

I have a 1992 Yukon 2DR 4x4. I've only had it a couple of months. I *thought* the 4WD worked, but today when we got a record snow fall I found out that it doesn't. The front wheels don't pull at all. The front driveshaft is spinning.

What do I check and where do I start? I think there is supposed to be an actuator on the front diff, but I'm not sure where. Does it go in from the passenger side and point towards the drivers side with two wires going in (one black, one black with a white stripe)? If so I been laying in the snow...since it's stuck in the street, trying to get a voltmeter to read anything on either wire. Its so cold, I don't know if I just didn't get the wire punctured enough or if there is in fact no voltage going to it. The key is ON and the lever is in 4L.

I'd really appreciate it if you guys can point me in the right direction. This is the first 4WD I've worked on. Thanks.

 

[Mean Green]

Okay to start with yes that is the actuator, I'm not sure on what colors the wires are but your described the right location. Is the light representing the front axel on the 4X4 indicator on? Secondly have you checked the fuse, in the fuse box, to see if it was blown? If the fuse isn't blown, take the actuator out and see if its extended or not. It SHOULD be if the truck is in 4Hi or 4 Low. If its not, it's most likely the actuator. Its a piece of cake to pull out and replace. Also if your using a volt meter just pull off the two pin plug that plugs into the actuator and test it using the contacts there, that will be easier then trying to probe the wires. Hope that helps you out!

 

[code.mafia]

Fantastic! That's the info I was looking for. No the front axle part of the display has never lit up. I checked all of the fuses in the dash panel less than a month ago. Have had to fix many small issues on this truck so I was looking for other things when I checked them all. I've heard about a possible thermal fuse? Does this truck have one and if so, where is it located? I will try checking voltage at that connector. I'm getting ready to go crawl around in the snow underneath it. Thanks!

 

[Mean Green]

If the light isn't lighting up on the 4X4 indicator, your actuator is most likely shot. But before replacing that, check the 4X4 fuse again. Because if that is blown, it wont do any good to see if your getting power there if no power is getting sent there. I have never heard of a thermal fuse on these trucks, i guess its possible there is one but I've never came across one. I'm swinging towards thinking the actuator is your problem, they seem to go out quite often.

 

[code.mafia]

I think the thermal fuse was a thread on an older truck. I pulled the actuator, no movement, but no 12v either. Found an empty spot in the fuse panel marked 'tran'. I'm going to put a fuse in it and see what happens. My fear is that the previous owner put a TrueTrac and 4.10's in the back and then didn't put matching gears in the front. Going to see...

 

[code.mafia]

Its not that, there's no wires hooked up to the 'tran' slot. I did find a 25A fuse in the 4WD slot and it was good. SO where does the wire from the actuator run to? It appears to go to the speed sensor or whatever it is on the rear of the transfer case?

 

[code.mafia]

Anyone have a wiring diagram for the 4WD system? I saw on another post there is a fluid pressure switch on top of the diff that power has to go through first. I'm going to go out and see if I get 12v at its connector. I just can't tell where the wiring goes. It looks like it runs from the actuator to the transfer case, but where does it go back inside to the fuse panel? I really need a diagram. I am trying to keep from peeling all the split loom off of all the harnesses down there.

 

[code.mafia]

I have 4.8v at the actuator. So does that mean there's not an open short right? But maybe some other component in front of it that is bad? I got zero voltage at the other connector which I think is a fluid pressure switch on top of the diff? There are only two wires going into the connector but 3 wires coming out and going to that sensor.

 

[code.mafia]

Turned out to be the ball-switch on the transfer case. 3 days of wrenching in the snow and a $6 part fixed it. That never happens to me, it's always the $700 part.

 

[Davidk3500]

Turned out to be the ball-switch on the transfer case. 3 days of wrenching in the snow and a $6 part fixed it. That never happens to me, it's always the $700 part.

Where is the ball switch located? I'm driving a 94 one ton dually 4x4 floor shift 4x4.