2003 Limited V8 4x4 (in theory)
I purchased this used a year ago. 4 wheel drive has never worked. When I test drove it, I put it in a dirt lot and shifted to 4 low, and got low range, so I assumed the transfer case, motor and related electronics were working (didn't seem right to go attempt a mud pit in someone else's truck). Since then I've determined that the transfer case does not engage the front driveshaft under any circumstances (either shifting it manually or relying on ControlTrac on a slippery surface). I have confirmed that the front axle and hubs are good, as I get driveshaft movement up front when spinning the front tires by hand. It's common for the 4x4 control module to go out, so that was replaced, but no luck.
Another issue that might be related - on initial acceleration i have a groaning sound and associated minor vibration that clears within a couple of seconds. This has been increasing in frequency and severity lately. I read on another board I post on that it might be caused by a faulty 4x4 module trying to engage the transfer case.
Since I can get low range, I assume the shift motor is good. Any suggestions on what else to look for?