I'll start off with a little history. My 97 4.0 SOHC control-trac has been experiencing a 4x4 bug. At first it showed up through the 4x4 only working when the truck was cold. After the truck would warm up, it would no longer work. I bought a service manual and followed the pinpoint test in order to identify the problem. Here is a short list of what I tested and the results:

- The brown wire that activates the clutch was reading only 4.5V when the selector switch was set to 4x4. (its supposed to read 12V according to the manual)

- The 4x4 and 4x4 Low lights work properly. No flashing or other indications of a problem.

- The 4x4 low actuator motor works properly. It shifts the T-case into low but only 2wd.

- The solid state clutch relay checks out ok per the manual's method.

- There is 12V to the solid state clutch relay.

- There are no shorts in the brown wire that delivers power to the T-case clutch.

This all led me to the conclusion that the GEM is faulty (per the manual) so I replaced the GEM and the 4x4 still does not work properly. I am about to bring it into the dealer and just suck it up. I have a few questions before I take the leap.

1. Could a faulty vehicle speed sensor (used for the control-trac) cause the GEM to not engage the T-case clutch?

2. If I were to bypass the GEM to engage the cluch would it cause any damage? I am thinking about installing a switch and standard automotive relay to supply 12V directly to the brown wire that activates the clutch.

Thanks for the help.

Dave

 

You are correct, you must have battery voltage to the clutch pack when the switch is in the 4x4 position.


No, the speed sensor only allows adjustment of power to clutch when in auto mode.


You could backfeed the T/C clutch, but you would no longer have the advantage of ControlTrac. You would however, add 2x4 low availability.

 

So the GEM does not "control" the amount of torque transfer when the truck is in 4x4? (i.e. it locks up the T-case)