When the ignition is switched to the ON position, the body control module (BCM) supplies 12 volts to the theft deterrent exciter module. The BCM also provides a low reference for the exciter. With the voltage supplied to the exciter, 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 BCM. The BCM then compares this value to a value stored in memory, the learned key code. If the value received matches the stored value, the BCM sends the fuel enable password to the engine control module/powertrain control module (ECM/PCM) via serial data.

Ignition is in the Accessory or Run position.

The transponder value received by the BCM is incorrect or not learned to the vehicle.

Schematic Reference

Immobilizer Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Immobilizer Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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 10-Minute Vehicle Key Relearn procedure. Refer to Replacing Keys .
2. While viewing the scan tool BCM VTD States parameter, turn ON the ignition with each of the available vehicle keys. The parameter should read Valid Key Code with all available keys.

⇒	If not the specified value, replace the appropriate key.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Replacing Keys