A4WD Concern

I have a 2002 TB EXT LTZ that I've been very happy with. I did encounter some of the common problems that others have (crazy remote mirrors most notably) but nothing serious, and the dealer made the necessary repairs. The concern I have now is with the A4WD mode. When I'm driving in A4WD mode, I feel a slight "thumping" every few seconds. I'm not sure if this is part of the mechanism that checks if 4WD mode is needed. I have no problems in 2HI, 4HI or 4LO, and I'm not a very trusting person, so I usually go right to 4HI in adverse conditions. I'm just concerned that this may be a warning of things to come? Any have any helpful information? I'd appreciate it!

I had the same experience. Felt like a skip or surge in AWD. I drove about 2500 miles without using the transfer case at all. I decided to try it the other week during the rain and it works without a hitch now. No explanation, but I smell a computer glitch. My mirrors are crazy too.

I had the same experience. Felt like a skip or surge in AWD. I drove about 2500 miles without using the transfer case at all. I decided to try it the other week during the rain and it works without a hitch now. No explanation, but I smell a computer glitch. My mirrors are crazy too.

Doesn't feel like a surge or slip. Just a mild "thump" every few seconds. Seems to operate OK. Maybe I should take it on mud to force the A4WD to shift into 4WD and see what happens.

As far as the mirrors, this is a defect and your dealer should replace your mirror motors. Mine work fine now.

I noticed a thumping, and felt the A4WD the most, and never noticed any noise or feel when the Trailblazer was in 2H 4H or 4Lo

I had contacted Chevy and found out that it's normal to feel or hear (the thump) of the transmissioni going from 2H into 4WD when it senses the changes in road conditions. One particular drive, it shifted and made the thumping sound once when i got on a highway during heavy rain, and didn't do it again till i got onto local roads, then would make that sound when I seemed to change speed or go from stopped at a light to motion.

Was told it's normal

Thanks for the info. I'm still a little concerned however, because the "thumping" is constant -- every 10 seconds or so -- on dry road. I guess it could just be the "sensor" checking the wheel speed, but I'm just not sure. I may have to (shudder the thought) bring it in to the dealer. Thanks!

I had a similar problem in which my Service 4WD light came on about 4 times within a week and by the time I got my vehicle in for service, my transfer case had to be completely replaced along with the selecter switch (costing over $1,300). I had 47K miles at the time. As told by the manager of the service department, who had been there many years and whom owns a 4WD chevy vehicle himself (we live in Anchorage,AK), the reason my 4WD went out is due to excessive use of the Auto 4WD selection on the switch. He said that the auto 4 wheel drive option will switch in and out of 4 wheel drive so much that the transfer case will wear out prematurely. I would say. And a convenient number that 47K....Just a few more than the 36K warranty. The service manager actually told me that he has seen it often enough that he wont even use the Auto 4WD option.
As a side note, the paint has been chipping off the door panels down low where road debris has been hitting it. This may not sound like an unusual problem, but look at similar SUVs with many more miles and the vast majority of them dont have half as many chips. The district manager of Chevy for my area refused to even look at my vehicle and dismissed my complaint. I owned a Grand Cherokee for 5 years and 89K miles with hardly any paint chips so it isnt my driving style (which is in a city with few rocks on the street). This is all despite the fact Chevy had distributed a service bulliten to all the dealerships stating that the district manager should look at any Trailblazers where paint chipping had been complained about in the same specific areas of the vehicle as mine. Obvioulsy there had been enough complaints for Chevy to produce the service bulliten, but someone on the corporate level stated that the final decision on whether or not to repair the paint on those panels. Gee I guess their hands are tied