I have a 1999 that will not shift into auto 4WD, 4Hi, or 4Lo. I've tried to shift while rolling without success. I don't even hear it trying to shift. When I press the buttons, the light flahes for a few seconds and then 2Wd light illuminates again. Anyone know what the problem might be?

 

Could be quite a few different things. The place to start is with cleaning the electrical connections at the TCCM and at the encoder motor on the side of the transfer case.

It would not hurt to see if there are any stored codes in the TCCM. You need a full feature scan tool for this though.

 

very hard to diagnose without looking at it, but it could be the motor on the transfer case that does the shifting, it may be worth it to bring to a shop and have them diagnose it for you or you could get a used one from a junkyard and throw it in to see if it fixes it

 

also you could try tapping that motor with a hammer while someone pressed the 4wd button it might just be stuck from not being used in awhile and the shock from the hammer can sometimes free it up

 

Check the fuse.

I've got a '97 that did the exact same thing and it was a blown fuse.

 

thanks for the suggestions. I'll let you all know what the outcome is.

 

i shift into 4x4 and it moves a bit then locks up for some reason but shifts back into 2wd , any idea whats going????

 

Sparrow, sounds like you have an encoder fault. The encoder is most likely losing track of what the motor position is and reverting back to the 2HI position. This is a common failure. But check over all of your electrical connections first.

 

Ok, so after finally completing other repairs on my truck I am ready to attack the 4WD. I opened the fuse box to check the fuse, but could not figure out which fuse was the right one. The diagram on the inside of the fuse box is only a little help, but I have not been able to figure out where the correct fuse is. Any answers on where I could find it or what abbreviation on the diagram is the correct one? Thanks

 

ATC - 20A

The diagnosis of the NVG 236 transfer case can be quite difficult. Aside from checking the resistance on the selector switch and back probing connections at the TCCM to monitor the encoder channels, most everything else has to be done with a scan tool.

Your problem could be a failure in the front axle engagement mechanism though. You should check to see if the cable to the actuator under your battery is free to move and engage the front axle.