One problem related to abs brake fail has been reported for the 2004 GMC Sierra. The most recently reported issues are listed below.
When returning from a trip, the truck was shut off and the ignition key was removed. The truck continued to run, flashed code p0758, check 4wd, check brakes, abs failure. The truck did this for two days while driving home and would stay running without the key from 2 to 16 minutes and could be put into gear and driven, all without the key.