Testing expensive looking 4wd part

My 4x4 is not working in my 02. Push the button on the side of the t case shifter, no light, no 4wd. The only thing I can think of is I got the 4wd comp that sits on the passenger side wheel hump under the hood, next to the fire wall. I'd like to see if there is a way to test it before I assume that's it. The fuse under the dash was fine.

 

The light doesnt turn on till engagement into 4x4 is complete.

Lift front end of truck off ground. Press 4x4 button.

If you can spin front driveshaft by hand then t-case isnt engaged.

If you spin passenger side wheel and the other wheel or driveshaft doesnt spin the add actuator isnt engaging.

If both arent engaged then its electrical.

If it was the button itself it would still go into 4x4 when t-case is put into 4-lo.

 

take some pictures of the part youre wondering about and ill see if I can identify what needs to be done to test it. .

 

The most common culprits on your year are the electric t-case actuator, driver side side of t-case and/or the electric front diff actuator. Failure of the 4wd ECU is extremely rare, just above "never happens" and they are located in the cab.
Follow Mr devins list for initial troubleshooting.

 

Ok so I just did the tests as stated above. Front wheels off the ground I can turn the front drive shaft by hand. When I spin the drivers side wheel, the passenger side does not move.

I noticed the little vacuum line the goes to the black "box" on the drivers side of the t case was undone.

I noticed yesterday when the problem presented itself that on the bundle of wires going along the drivers side rocker, under the long plastic trim piece, the black wire was broken by all but a few strands. I had spare wire so I temporarily spliced it in with no change in the 4wd. Pic below.



Here's the expensive looking part that I suspect may have gotten wet.

 

This is the ABS controller. It's not directly related to engaging 4WD.

 

Can you spin the driveshaft when in 4x4 and tires on the ground? I had an issue with the GF's 4x4 engaging on a trail and the front driveshaft was able to spin. A few light blow with a hammer loosed the actuator and it engaged.

 

Was the 4WD button depressed when you did this? What changes in this scenario if you move the lever forward into the 4lo position?

 

ahhh good to know. I saw 4wd on it and just assumed.

 

Ok, just did more tests. Drive shaft spins freely by hand with the truck on the ground in 4hi. Jacked it up, trans in N, shifter the t case to 4lo. Can still spin the front drive shaft by hand.

 

yes the button was depressed.

 

If the driveshaft can be turned when in 4wd, trans in gear or auto in park, the t-case has not actually shifted into 4wd.
That hose on the t-case actuator is a breather not a vacuum hose. If it was off water could have gotten in. The actuators suffer from water intrusion/corrosion on a good day even with the breather hose in place.

Sequence of operation-----------push button, the t-case 4wd actuator shifts case into 4wd, if that happens the 4wd (condition) switch then allows the ADD actuator on the diff to engage, if that is successful the 4wd switch on the front diff will light up the lamp. This is independent of 4hi/4lo.

A guess from afar would be the t-case actuator is on sick leave.

 

Very much appreciated. Is there a way to test the actuator or should I just start looking for a replacement? Thanks again!

 

I just found a thread on the subject and some say the actuator is on the front diff. So is it on the t case or front diff?

 

Your year has 2 actuators, both electric. One on the t-case (engages the front driveshaft) and one on the pass side of the front diff that "connects/disconnects" the front diff.
Both must function for 4wd in the order I mentioned. A failure anywhere in the sequence will result in no 4wd. Remember the t-case must shift into 4wd first (no can spin driveshaft).

Many times folks get away with a good "take apart and clean" operation. Read up on the threads for cleaning up the t-case actuator first.

 

Popped off the rear add on the t case. There was water in there. Dried it and removed the nasty yellow grease. Cleaned it up and applied dielectric grease in its place. Now I need help putting it back together. The only way the two halves meet is if I twist them slightly and they mate up. Trouble is the bolt holes are slightly off where I can't get them in. Do I force it? Here's where I'm at now

 

Ok, got that figured out. Now to get it back on the shaft sticking out of the rear of the t case. Any suggestions?

 

GOT IT! I had take the clamshell (actuator) back apart. Then I turned the big plastic gear by hand until it crawled along the shaft and seated. 4x4 light works in 4hi and lo. Feels like I have 4x4 again. Gonna jack it up and test it for sure.

Now my diff lock light just blinks when I try and activate it. Related?

 

Scratch that. Diff lock works now. 4hi and 4lo work. Seems like all is right with the world and I can drive to work now hahaha

Thanks to everyone who helped. You guys saved my ass!

 

Hello Trapperr, please tell me how to remove the actuator (the one that has a large plastic gear). It's stuck and I do not know how to release it. I have turned the big plastic gear by hand, but nothing happens.