Buick Regal: DTC B2580 or B3866 (T4L)

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 B2580 00

Left High Beam Control Circuit Malfunction

DTC B3866 00

Right High Beam Control Circuit Malfunction

Circuit/System Description

The high beam and flash to pass functions are contained within the turn signal/multifunction switch. The body control module (BCM) provides the turn signal/multifunction switch with two signal circuits, the high beam signal circuit and flash to pass signal circuit. When the low beam headlamps are ON and the turn signal/multifunction switch is placed in the high beam position, ground is applied to the BCM through the high beam signal circuit. The BCM responds to the high beam request by sending a message via high speed bus to the headlamp control module. The headlamp control module then communicates via private CAN bus with the left and right high beam control modules to illuminate the high beam LEDs.

Conditions for Running the DTC

• Battery voltage must be between 9 - 16 V.
• High beam headlamps ON.

Conditions for Setting the DTC

DTC B2580 00

The left headlamp high beam control module detects an internal malfunction in the left high beam control circuit.

DTC B3866 00

The right headlamp high beam control module detects an internal malfunction in the right high beam control circuit.

Actions Taken When the DTC Sets

• The driver information center will display Advanced Front Lighting System Fault.
• One or more high beam LEDs are inoperative.

Conditions for Clearing the DTC

• The condition responsible for setting the DTC no longer exists.
• A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

Diagnostic Aids

DTC B2580 or B3866 will set when one or more of the left or right high beam LEDs are inoperative. No parts are serviceable within the headlamp assemblies so complete headlamp assembly replacement is necessary. The appropriate K135 Headlamp Low Beam Control Module, K191 Headlamp High Beam Control Module, and K166 Multifunction LED Control Module may be reused when replacing the headlamp assembly.

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 Testing

1. Ignition ON.

2. Verify DTC B2580 00 or B3866 00 is not set.

• If DTC B2580 00 or B3866 00 is set

1. Replace the appropriate E13 Headlamp Assembly.

• Go to next step: If DTC B2580 00 or B3866 00 is not set

3. All OK

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Headlamp Replacement

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