The service 4WD started appearing in the driver information display intermittently. Taking the vehicle in for service gave no relief. The vehicle started acting erratically, slipping in and out of gear intermittently. It wasn't safe to drive anymore, ie stranded at stop lights or after slowing for traffic it had no acceleration. It became clear at this point that the problem wasn't going to be able to be diagnosed at a repair facility, without replacing parts needlessly and then test driving the vehicle until it worked again. I started checking on line and found many of these vehicles exhibiting the same behavior and traced the problem to a defective encoder motor which fixed the problem I feel the way the vehicle acted with this problem is a very unsafe condition and should have a fail safe built into it to at least prevent complete loss of acceleration. At the very least owners should have been warned of this possible situation since there are technical service bulletins out on this condition.

- Grandview, MO, USA

"service 4WD" started to be displayed erratically in the dic. 4WD system started to function erratically 4WD control switch witness lights light erratically or do not light at all. 4WD low range engaged by itself unexpectedly while driving - this was a serious accident hazard, fortunately it occurred at low speed and at a place where the vehicle could be stopped safely. General Motors has issued tsb 05-04-21-003C (April 15, 2008) for this condition however owners were not notified about it or the potential associated accident risk. Research on the web at vehicle owner clubs shows this condition to be a very frequent problem for GM vehicles using the this type of 4 wheel drive. Further research on the same sites suggests that the solution to the problem was a challenge to GM and it was a "hit-and-miss" approach with multiple trips to the dealer to get it resolved. This malfunction could be cause a serious accident if it happens at interstate speeds in heavy traffic or on a slippery steep mountain road ( just to give a few examples).

- Salem, OR, USA

I own a 2005 Avalanche with 2000 miles on it. When turning sharply while in 4 wheel drive, going forward or in reverse, the truck bogs down and stops. There is nothing in the owners manual about this. This is a dangerous condition for someone who does not realize what will happen. If I were to make a U turn the vehicle will come to a stop if the wheels are turned two sharply. My dealer did not even know about this untill I brought it to his attention.the dealer went out on his lot and drove an Avalanche in 4 wheel drive to determine if I was nuts or not. Well I am not nuts as thiers did exactly what I said. The dealer then contacted General Motors and was told this condition is normal so the U joints and gear box will not be damaged. If they say it is normal to lock up why don't they put it the owners manual? someone is going to be seriously hurt over this condition and it will be more than U joints or gear box.

- San Antonio, TX, USA