Ford Explorer: 4WD and 4WD LOOW lights flashing

In the '95 models of Control Trac the 4WD system had a 2WD mode and a
4WD-Auto and 4WD-Lo mode. The transfer case clutch pack was pulsed by
the GEM system in response to differential speeds of the front and rear
driveshafts in the Auto mode. The system starts at around 10% engaged
and increases the engagement period in roughly 10% increments until rear
wheel slippage is stopped. If the system detected something odd, like
the back going faster than the front even after reaching 100% engaged
then the system flashes the 4WD and 4WD-Lo lights to alert the driver of
a problem. In the '95-'96 models I believe the failure mode is 100%
engaged in the 4WD positions, so you will still have 4WD, but only for
use off pavement. Usually the problem is with one of the speed sensors,
but dirty contacts could also cause this. God Luck!

=Vic=
Bear Gap, PA

FS wrote: 

FWIW, I experienced the exact same thing. What Vic describes is I what I've
heard as the problem as well. I checked my sensor contacts, and they were
fine. Next step is to remove the sensor assembly for the front driveshaft
(from the transfer case) and see if it's gummed up or dirty. If cleaning
the sensor doesn't fix it, then I may have to replace the front driveshaft
speed sensor. I think what's happening is that we're gettting a sporadic
signal (or no signal at all) from the speed sensor on the front driveshaft
rotation speed. Therefore, the system, as Vic describes, locks up full 100%
because it thinks the rear driveshaft it spinning still, and thus we also
get the flashing dashboard lights as you describe. We have experienced this
lockup as well. If you drive on dry pavement under these conditions you can
hear the clutch packs groaning/slipping as you turn (probably designed as
relief so you don't snap an axle shaft). Still, not a particularly healthy
thing for the 4wd system so we leave it in 2wd for now, until I fix it. I
priced out a new sensor at AutoZone (or was it the Ford dealer?) and it was
about $65. Seems easy to replace, but I'd check the contacts first and then
pull the sensor itself to see if it's dirty. Per the shop manuals, the
sensor actually reads off a notched gear-like ring attached to the front
driveshaft just inside the transfer case housing. It's supposed to pick up
"pulses" a lot like how an ABS system picks up pulses to determine if all 4
wheels are turning at the same rate.

Mike


"Vic Klein" <net> wrote in message
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