WARNING: This page is about a different car, the 2002 Pontiac Sunfire and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Lock System Does Not Unlock Diagnostic Flow Chart (1 Of 2)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Lock System Does Not Unlock Diagnostic Flow Chart (1 Of 2)