One problem related to brake abs warning light has been reported for the 2003 GMC Safari. The most recently reported issues are listed below.
On vacation abs light would come on during driving. When braking, just before coming to a stop, more travel in the pedal and brakes chattered. Abs light might be on or off during braking. Went to dealer, right front sensor erratic. Replaced right front sensor. Works good again. Van has 32,000 miles.