I have a 2004 Envoy with 188,000 miles. I made a 4 hour trip the other day with several stops and everything worked fine until my last stop. When I started it the brake warning light, ABS warning light and the service 4WD light came on. The brakes seemed fine so I drove home. When I got home I tried to put it in 4WD but it would not engage even after moving it back and forth a little. I shut it off and the key would not go into the lock position so I could remove it even after restarting it and moving the shifter back and forth several times. The battery warning light stayed on so I disconnected it to keep it from discharging. I've looked at numerous threads about the key, but none mention anything about the warning lights. I suspect there's a computer problem. Any help would be appreciated.