4x4 Issues Solas Will Not Comm With Transfer Case

[speadphreak]

Hi! I hope someone can help. I have a 1999 GM K2500 8600lb crew cab 4x4 with a 5.7 ltr. I am having issues with the 4 wheel drive system. My truck is never used for mudding or any other abusive behavior (not that theres any thing wrong with that) it does tow once in awhile up to about 10k lbs, but generally not very far (30 40 miles). I have recently begun having issues with the 4x system. I can switch into 2hi and 4lo but I have no use of 4hi. When using 2hi the light is not on, on the switch(push button on the dash). When I am in 4lo both the 4hi and 4lo lamps, light for a moment then both go out as well. 4lo activates normally, stopped in neutral push the button and then I hear it clunk in. Swithching to 2hi is obviously the opposite stop, neutral, push 2hi. I have tried to engage 4hi running at speeds from 5 - 30 mph as well as stopped in neutral, and stopped in park(just to see if it would work) with no luck. My neighbor has one of the expensive Solas computers which diagnoses everything else just fine on my truck, but comes back with a cannot communicate with transfer case error.

 

I know the actuator works or I would not be able to engage 4lo. But I am at a loss as to where to look next, switch, TCCM, encoder motor, or maybe something else? I have read elsewhere about possible corrosion issues on the switch or TCCM connections, I have cleaned the switch connections with contact cleaner, and 2000 grit paper with no difference. I would do the TCCM but I dont know where it is located. Any help would be greatly appreciated, Thanks in advance. Mike