Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the exciter coils surrounding the ignition lock cylinder. The energized transponder transmits a signal that contains its unique value, which is received by the theft deterrent module (TDM). The TDM then compares this value to a value stored in memory. This stored value is the learned key code. If the value is correct, the TDM will send the pre-release password via the serial data circuit to the engine control module (ECM). If either the transponders unique value or the calculation to the challenge is incorrect, the TDM will send the start disable password to the ECM.

Ignition is in the Accessory or Run position.

The transponder value measured by the TDM is incorrect or not learned to the vehicle.

Schematic Reference

Theft Deterrent System Schematics

Connector End View Reference

Theft Deterrent System Connector End Views

Description and Operation

Vehicle Theft Deterrent (VTD) Description and Operation

Electrical Information Reference

Scan Tool Reference

Important: When using this diagnostic, more than one vehicle key is required to ensure proper diagnosis. If more than one key is not available at the time of service, contact the customer and ask if any other keys can be provided for service. If unavailable, a new second key can be created.

1. Perform the Replacing Keys procedure. Refer to Replacing Keys .
2. While viewing the scan tool Valid Key parameter, turn ON the ignition with all available keys. The parameter should read Yes with all vehicle keys.

⇒	If the parameter does not equal the specified value, replace the affected key.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.