One problem related to engine and engine cooling has been reported for the 2003 GMC Sierra. The most recently reported issues are listed below.
On February 18, 2003 I purchased a new 2003 truck the truck came with the service light on. When driving the 4x4 wheel light would come on as if the truck was in 4 wheel drive. The light would go off after stopping and shuting the truck off for at least 15 minutes. I went to the dealer and they said there was no fix at this time and they gave me a service bulletin, file in section:4-driveline axle bulletin no:03-04-21-001 date: February, 2003. I was told that if I was worried about the 4x4 engaging on its own while driving the only thing they could do was to disengage the 4x4 wheel drive at this time. I need to have the use of the 4x4 wheel drive as I own a large concrete construction company and use my truck all day long on jobsites. I left the dealer not knowing what to do. I was worried about damaging the 4x4 unit even more on my new truck. So two weeks later I was tired of worrying, so I took the truck back to the dealer and they disengaged the 4 wheel drive. The service 4x4 wheeel light is still on at this time. I also filed a complaint with GMC on 3/27/03 #1-85090755. I have not heard fron the dealer in one month.