2001 Blazer/Trailblazer, with the 4 button 236 transfer case. I've been chasing down problems without access to a code reader. Installed a new shift motor and it seemed to be working correctly up on stands. Pulled the battery cable to clear any codes left in the TCCM and when I hooked it back up, I hear the motor run. It had shifted to 4 wheel low by itself! What could cause this. Key was off and 4 wheel low had never been selected. This had never happened with the old motor.

 

Have you tested the switch resistances as registered at the TCCM? The switch communicates desired mode/range settings to the TCCM by altering the resistance of a known voltage source from the TCCM, thereby returning a lower voltage back to the TCCM. If the switch is somehow screwed up and/or there is corrosion at the plug on the TCCM, the TCCM could be seeing the voltage for a 4LO desired mode/range.