Buick Regal: DTC B259A or B259B

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 B259A 01

Left Cornering Lamp Relay Control Circuit Short to Battery

DTC B259B 01

Right Cornering Lamp Relay Control Circuit Short to Battery

Diagnostic Fault Information

Circuit/System Description

The daytime running lamp relay - left and daytime running lamp relay - right is supplied with battery voltage at all times. If the engine is running and the ambient light is day the body control module (BCM) energizes the appropriate daytime running lamp relay by applying ground to the appropriate daytime running lamp relay control circuit. When the appropriate daytime running lamp relay is energized, the relay switch contacts close and battery voltage is applied through the appropriate daytime running lamp relay supply voltage circuit which illuminates the appropriate daytime running lamp.

Conditions for Running the DTC

• The engine is running.
• Headlamp switch in AUTO position.
• The ambient light is day.

Conditions for Setting the DTC

The BCM detects a short to voltage on the control circuit.

Action Taken When the DTC Sets

The daytime running lamps are always OFF.

Conditions for Clearing the DTC

The condition for setting the DTC is not longer present.

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

Engine is running idle, supply sufficient light to the ambient light sensor to simulate daylight conditions.

The daytime running lamps should be ON.

Circuit/System Testing

1. Ignition OFF, disconnect the appropriate daytime running lamp relay.

2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 86 and ground.

• If the test lamp is OFF, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.

3. Remove the test lamp.

4. Engine running, headlamp switch in the AUTOMATIC LIGHT position.

5. Connect a test lamp between the appropriate daytime running lamp relay B+ circuit terminal 86 and the control circuit terminal 85.

6. Cover the ambient light sensor to simulate night conditions. The test lamp should be OFF.

• If the test lamp is ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 Body Control Module.

7. Supply sufficient light to the ambient light sensor to simulate daylight conditions. The test lamp should be ON.

If the test lamp is OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K9 Body Control Module.

8. If all circuits test normal, replace the appropriate daytime running lamp relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Relay Replacement (Attached to Wire Harness) Relay Replacement (Within an Electrical Center)
• Control Module References for BCM replacement, setup and programming

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