Buick Regal: DTC B3935

Diagnostic Instructions

• 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.

DTC Descriptor

DTC B3935

Transponder Authentication

For symptom byte information, refer to Symptom Byte List.

Circuit/System Description

Without BTM and/or ATH/ATS

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the key is energized by the exciter coil surrounding the ignition lock cylinder.

The transponder transmits a signal to the immobilizer control module. The immobilizer control module translates this signal to a serial data message which is sent to the body control module (BCM). The BCM then compares this value to a value stored in memory. If the value is correct, the BCM will send the prerelease 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 BCM will send the start disable password to the ECM.

With BTM and/or ATH/ATS

When a ignition key is inserted into the key pocket/slot and the ignition mode switch is pressed, the transponder embedded in the key is energized by the immobilizer antenna exciter coil. The transponder transmits a signal to the immobilizer control module. The immobilizer control module translates this signal to a serial data message which is sent to the body control module (BCM). The BCM then compares this value to a value stored in memory. If the value is correct, the BCM will send the prerelease 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 BCM will send the start disable password to the ECM.

Conditions for Running the DTC

• Ignition is in the Accessory or Run position.
• A valid transponder value has been read.

Conditions for Setting the DTC

The transponder calculation of the challenge from the BCM does not match the BCM calculation.

Action Taken When the DTC Sets

• Vehicle starting will be disabled.
• The security indicator will illuminate. The driver information center will display a service message.

Conditions for Clearing the DTC

• A current DTC will be cleared when a valid transponder value has been read and authenticated.
• A history DTC will be cleared after 100 malfunction-free ignition cycles.

Reference Information

Schematic Reference

Immobilizer Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEW INDEX

Master Electrical Component List

Description and Operation

Immobilizer Description and Operation

Electrical Information Reference

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

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Verification

1. Ignition ON.

2. Verify the scan tool Immobilizer Allows Engine to Start parameter is Valid when using each vehicle key.

• If Authentication Error

NOTE: Perform the appropriate key procedures for this vehicle. Not all vehicle models and years are the same.

Replace the keys.

• Go to next step: If Valid

3. Verify DTC B3935 does not set while operating the vehicle under the conditions for running the DTC.

• If the DTC is set

Replace the K9 Body Control Module.

• Go to next step: If the DTC is not set

4. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for body control module replacement, programming, and setup.

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