2000 Explorer XLT auto A4WD problem

[firefighter1]

I have a 2000 Explorer XLT with A4WD. The 4wd will not automatically engage when wheel slippage is detected. It will operate in 4 wheel high and low modes properly but not in auto mode. I can literally do a burnout with my right rear tire and the 4wd will not engage automatically. I haven't actually tried to force my left rear tire to spin on purpose but I believe it will. I don't think both rear tires will spin or burnout at the same time. I do know when on a wet surface and on a slight curve on a on ramp, that the back end will slip out and I will start drifting. Explorers don't drift well on wet pavement.
I did replace the transfer case about 4 months ago or so. About 5-7 clutch discs had disintegrated and it was staying in 4wd high and wouldn't come out. It was replaced with a used transfer case with matching numbers. The only difference was that the new/used case had a counter weight on it where mine did not and a lot less miles on it. Also replaced pinion seals and u-joints at the same time. AllDATA is no help with this unless I want to ohm everything. I am thinking possible a sensor on the transfer case but that will be hell to replace. The transfer case has to come apart for those sensors. The system did work before I replaced the transfer case but I can't say I remember it engaging automatically after the swap. Then again I had no place to test it at the time and didnt think much of it with the high and low working. Any ideas or thoughts anyone? I do have another GEM module but the numbers arn't matching up. Mine says XL2T-14B205-CD with the large C and says sport utility automatic A4WD at the bottom. The other one says P1F87B-14B205-CC with the big C and it says sport utility automatic 4WD at the bottom. I think it may have come out of a 98 explorer.

 

[drdoom]

Check the sensors, you don't have to pull the case to do this, but maybe the shift encoder might block access to the front sensor. Check to see if they are clean, and check the wiring harness also.

 

[firefighter1]

If I remember correctly the sensors will not come out of the transfer case to be checked without access inside of the case. The harness is good. I will pull the connector to check the pins.

 

[drdoom]

I have repaired a few of those, and one of the first things I do is strip the encoder and all of the sensors from the case, remove case from truck, THEN open the case.

 

[firefighter1]

I think I need to find the problem before throwing parts at it.

 

[firefighter1]

the connectors and sensors check out fine. The sensors ohm at about 7.55 and 7.45 for the other.