Buick Regal: DTC B258A or B258E

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 B258A 00

Left Low Beam Control Circuit Malfunction

DTC B258E 00

Right Low Beam Control Circuit Malfunction

Circuit/System Description

The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the headlamp switch is placed in the OFF position, the headlamp switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch in the PARK position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds to the low beam request by applying ground to the left and right low beam relay control circuits, which energize the left and right low beam relays. With the left and right low beam relays energized, the switch contacts close allowing battery voltage to flow through the low beam fuses to the left and right low beam control modules, which illuminate the low beam LEDs.

Conditions for Running the DTC

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

Conditions for Setting the DTC

DTC B258A 00

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

DTC B258E 00

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

Actions Taken When the DTC Sets

• One or more of the low beam LEDs are inoperative.
• The driver information center will display Failure Low Beam on Left Headlamp or Failure Low Beam on Right Headlamp.

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 B258A or B258E will set when one or more of the left or right low 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 B258A 00 or B258E 00 is not set.

• If DTC B258A 00 or B258E 00 is set

1. Replace the appropriate E13 Headlamp Assembly.

• Go to next step: If DTC B258A 00 or B258E 00 is not set

3. All OK

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Headlamp Replacement

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