Pops54

The 4wd engages randomly after sitting overnight.
Sometimes this happens after driving for awhile. The 4wd high & 4wd low
lights sometimes blink when this happens. Any suggestions as how to fix or
what causes this problem...

Vic Klein

The blinking lights are a signal from the GEM computer that the 4WD system
has a problem. Most of the time it is a disagreement in the data from the
front and rear driveshaft speed sensors, either from a failure of the
sensor, a bad electrical connection, or crud building up on the inside gear
(tone wheel) that the sensor looks at to get the speed. These are mounted on
the transfer case and would be the first place to look.

Essentially, the Control Trac system watches the speed difference between
front and rear wheels and if the rear seems to be going faster than the
front (slipping), then it increases the duration of the transfer case clutch
engagement puls to increase the amount of power to the front wheels in 10%
increments. When the rear is equal or less than the front, it starts backing
off again. If it gets to fully engaged (like when selecting 4WD-Hi) and the
rear still seems to be faster than the front, it realizes that is not
possible, flashes the lights, and disengages the 4WD. Good luck, it
shouldn't be a big deal to repair.

=Vic=
Bear Gap, PA

"Pops54" <rpear7108@nospam.aol.com> wrote in message
news:831cdf52c928b602c2d9235144f2f188@localhost.talkaboutautos.com...
> The 4wd engages randomly after sitting overnight.
> Sometimes this happens after driving for awhile. The 4wd high & 4wd low
> lights sometimes blink when this happens. Any suggestions as how to fix or
> what causes this problem...
>

Pops54

Thanks, I will start there. I drove it last night, everything worked fine
again. This all started after a 500 mile trip. It has 90,000 miles on it.

Rick...