I've got a 99 jimmy with the NP8 case in it. As some of you are aware, my 4wd has not been working for some time now.

At first, the tccm would click when I hit the buttons, but do nothing. I have already verified that the vaccum side of the system functions correctly.

For the last little bit, when I hit a button, the tccm does not click anymore, but i DO hear the solenoid that is on the firewall. Any predictions as to what the problem will be??

I'm kinda thinking that it will be both the tccm and the encoder.....I'll know soon enough. Also, as I'm driving, the service 4wd illuminated by itself. that's why I'm thinking tccm......

 

Report back once you have the codes from the TCCM. They'll likely point you in the direction of the failed or failing component.

 

Well, I just got back from the transmission shop...good lord! The codes they came up with are as follows:
-c0387
-b2725

The also magically got the truck to go into 4wd, but could not get it out. They ended up taking the front drive shaft out for my trip home.

Any thoughts? They're thinking it's probably a bad ground somewhere.....

 

From the OBD2 DTC Section:
B2725 - Active Transfer Case Mode Switch Malfunction
C0387 - Unable to complete shift

Also a few searches for you to see what others may have done when encountering these codes: C0387 & B2725

From the codes, you may have two problems with the system.

After reading through the material presented above, I would then pull the connector at the TCCM & inspect it for corrosion. Corrosion is the most likely cause of a B2725 problem and could cause a C0387 code if insufficient voltage is being sent to the encoder motor.

 

Thanks for the quick reply. I have checked the harness many times when this issue first arose. I did find some corrossion and cleaned as required- however it didn't seem to help much.

After reading through a few posts, it seems that it should be either the tccm or the switch on the dash itself. I'll have to review the section that talks about checking switch resistance to eliminate the switch.....do you agree?

Thanks again...oh, off the top of your head, is there a "common" ground problem with these systems?