With Centering Window And Service Lock
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 GMC C3500 HD, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Hold SIR coil face up. See Figure. While depressing service lock, rotate coil hub clockwise until it stops. Rotate coil hub counterclockwise slowly until centering window appears Yellow and line-up marks are aligned. Release service lock.