• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

For symptom byte information, refer to Symptom Byte List.

When certain modules are programmed and configured during installation, the module learns a specific environment identifier which is unique to the vehicle. The environment identifier is used to prevent the swapping modules between vehicles. The body control module (BCM) is the keeper of the environment identifier. The instrument cluster, electronic brake control module, HVAC control module, inflatable restraint sensing and diagnostic module, engine control module (ECM), and steering column lock module (if equipped) each learn the environment identifier during their configuration process. During vehicle operation, the BCM sends the immobilizer identifier as a challenge and each module responds to the challenge by sending the environment identifier back to the BCM. If the BCM sends an incorrect immobilizer identifier or a specific number of incorrect environment identifiers are received, vehicle starting is disabled.

Ignition is in the ACCESSORY or RUN position.

The control module's environment identifier does not match the environment identifier stored by the BCM.

• The security indicator in the instrument cluster will illuminate.
• Vehicle starting will be disabled.

A current DTC will be cleared when the module learns a correct environment identifier.

Immobilizer Schematics

Master Electrical Component List

Immobilizer Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Control Module References for scan tool information

1. If two or more of the following DTCs are setting not related to a BCM replacement procedure (DTC B3924, DTC B3925, DTC B3926, DTC B3927, or DTC B3928) address those DTCs before attempting to address DTC B3902. Refer to DTC B3924-B3928.
2. Perform the Programming and Setup procedure for the control module that set DTC B3902.

Note: When performing the following step, Immobilizer System Component Programming, the module may also need to be reset by using the SPS function Prepare For Removal.

3. Perform the Immobilizer System Component Programming Immobilizer System Component Programming.

Note: If the Immobilizer System Component Programming with existing keys procedure does not work then perform the procedure for new keys but continue to use the existing keys.

4. Verify DTC B3902 does not set after programming.
• If the DTC sets after programming

  Replace the control module that set the DTC.

• If the DTC does not set after programming
5. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for instrument cluster, electronic brake control module, HVAC control module, inflatable restraint sensing and diagnostic module, engine control module, or steering column lock module replacement, programming, and setup.