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 fuel continue password via the serial data circuit to the engine control module (ECM). If the learned key code does not match or a transponder value is not received, the TDM will send the start disable password to the ECM.

The TDM is unable to communicate or learn the key.

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

Replace the suspected inoperative or malfunctioning key. DTC B3935 should not reset and the vehicle should start.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Important: Because of how vehicle key information and theft deterrent passwords are stored within the TDM, the Set Up a New Theft Deterrent Module procedure must be performed prior to the removal and replacement of the TDM if the vehicle keys are being reused. Performing the setup procedure first allows the scan tool to extract the key information and passwords from the old TDM prior to its removal. Failure to perform this step will result in the failure to learn the existing vehicle keys and new vehicle keys will be required when replacing the TDM.