[njyahoo]

It's times like this that one has to dust off the old schematics (wiring diagrams) roll up the sleaves and start troubleshooting. Unfortunately too many people depend on computers to do that for us. If you can get your hands on a Haynes service manual there is a wiring diagram in the back with a troubleshooting guide. Tough part is finding someone who can read the diagrams.
DC is simple... current that leaves the + pole of the battery has to get back to the - pole of the battery. All vehicles use the metal chassis (body) as ground (- pole). So that means 99.9% of all wiring is attached to the + pole. The exception to this rule is generally green = ground = - pole. All current comes from the battery power source to a switching device (control) and then to the device being activated (load = lights, motors, etc) and then to ground. A short circuit is when power bypasses the load and goes directly to ground (blown fuse). An open circuit is when there is a break in the wire, the control fails, or you lost ground so the device doesn't get power. This is as simple as I can make it.
Now for your problem...since the computer has no stored code then you need to look at what would cause a disruption in the circuit but not cause an error. I would start with an intermittant problem like a loose connection either from the battery + post or to ground. You need a closed loop from the battery to keep things active. I would suspect something like a loss of power to the computer module that controls the AWD function. The symptoms would mimic what happens when you cycle the key switch off then on again. The dash displays flash to let you know they are functioning.
This is the best I can do without access to a wiring guide. I hope this can get you somewhere in the ballpark. One very important thing to look for first is a loose or corroded ground wire. 9 times out of 10 it's a bad chassis ground that causes the most intermittant problems in automobiles due to exposure to the elements or loose connections.