WARNING: This page is about a different car, the 2004 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: No Response From Sentry Key Immobilizer Module - Diagnostic Procedure (Test Steps 1 - 4)
Courtesy of DAIMLERCHRYSLER CORP.
Fig 2: No Response From Sentry Key Immobilizer Module - Diagnostic Procedure (Test Steps 5 - 6)