Perform the Diagnostic System Check - Vehicle .

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 energised by the exciter coils surrounding the ignition lock cylinder. The energised 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 start enable 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 ACC or ON position.

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

Scan Tool Reference

Control Module References

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. Attempt to start the vehicle. The vehicle should start with all available keys.

⇒	If any keys result in inoperative starting, replace the suspect key.

Perform the Diagnostic Repair Verification .