Buick Regal: DTC B257C or B257D

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 Descriptors

DTC B257C 00

Left Headlamp Assembly Malfunction

DTC B257D 00

Right Headlamp Assembly Malfunction

Circuit/System Description

The headlamp control module calculates the headlamp angle and sends commands to the left and right adaptive forward lighting system headlamp actuators. The headlamp actuators drive the headlamps to the position commanded by the headlamp control module. The headlamp control module monitors the headlamp actuator motor control circuits for proper circuit continuity and for shorts to ground or voltage. If a malfunction is detected, a DTC will be stored in memory and the driver will be notified with a "Service AFL Lamp" message displayed over the driver information center located on the instrument cluster.

Conditions for Running the DTC

• Battery voltage must be between 9 - 16 V.
• Engine RUNNING.
• Headlamps ON.

Conditions for Setting the DTC

DTC B257C 00

The headlamp control module receives a serial data message from the left headlamp internal logic module that an internal headlamp malfunction has occurred.

DTC B257D 00

The headlamp control module receives a serial data message from the right headlamp internal logic module that an internal headlamp malfunction has occurred.

Actions Taken When the DTC Sets

• The headlamp control module disables the AFL system.
• The driver information center will display AFL Lamps Need Service.
• On vehicles equipped with both AFL and headlamp leveling, the headlamp leveling system will remain active.

Conditions for Clearing the DTC

• The condition responsible for setting the DTC no longer exists.
• A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.

Diagnostic Aids

DTC B257C and B257D will set when there is an internal malfunction within the left or right headlamp assemblies. No parts are serviceable within the headlamp assemblies so complete headlamp assembly replacement is necessary.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) Wiring Schematics

Connector End View Reference

COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

Exterior Lighting Systems 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 DTC B257C or B257D is not set.

• If DTC B257C or B257D is set

1. Program the K26 Headlamp Control Module.
2. Verify the DTC does not set.
   • If the DTC sets, replace the appropriate E13 Headlamp Assembly.
   • Go to next step: If the DTC does not set
3. All OK.

• Go to next step: If DTC B257C or B257D is not set

3. All OK

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Headlamp Replacement
• Control Module References for Headlamp Leveling Control Module replacement, programming, and setup

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