I have a 2004 Envoy XUV with 4WD that won't engage, although the proper switch lights do illuminate as intended. Further, I have no "service 4WD light" and have listened for and heard the two distinct activation sounds from the encoder motor and the front axle actuator. So, I've gone through the offroadtb.com 4WD flowchart diagnosis and have discovered the following: the front prop-shaft rotates as I rotate the lifted right front tire (does same with the left tire when lifted - both with no unusual sounds coming from the front differential, actuator housing, or elsewhere for that matter), which, according to the flowchart, seems to indicate a problem with the transfer case. Is there still a possibility that either the TCCM (I did the 30 second pull of fuse #8), the encoder motor 'brake' or something electrical is the problem. I hate to take it to the dealer for diagnosis at $129/hour.