Sir Diagnostic System Check: Notes
WARNING: This page does not describe the selected car, but rather 12 other vehicles, including the 1999 GMC Yukon, 1999 GMC Suburban, 1999 GMC Sierra, 1999 GMC Pickup, and 1999 GMC Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
WARNING:
To avoid air bag deployment and injury when trouble shooting system, only use test equipment specified in diagnostic charts. Carefully follow all instructions.