Buick Regal: DTC B25F8 or B25F9

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 B25F8 01

Left Headlamp Relay Control Circuit Short to Battery

DTC B25F8 02

Left Headlamp Relay Control Circuit Short to Ground

DTC B25F8 04

Left Headlamp Relay Control Circuit Open

DTC B25F9 01

Right Headlamp Relay Control Circuit Short to Battery

DTC B25F9 02

Right Headlamp Relay Control Circuit Short to Ground

DTC B25F9 04

Right Headlamp Relay Control Circuit Open

Diagnostic Fault Information

1. Headlamps Malfunction

Circuit/System Description

Automatic Headlamps Without CE1

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 the 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 and 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 low beam relay control circuit which energizes the low beam relay. With the low beam relay energized, the switch contacts close allowing battery voltage to flow through the low beam fuses to the low beam control circuits illuminating the low beam headlamps.

Automatic Headlamps With CE1

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 rain sensing module to determine if the 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 and 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 low beam relay control circuit which energizes the low beam relay. With the low beam relay energized, the switch contacts close allowing battery voltage to flow through the low beam fuses to the low beam control circuits illuminating the low beam headlamps.

Conditions for Running the DTC

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

Conditions for Setting the DTC

DTC B25F8 01

The BCM detects a short to voltage in the left headlamp low beam relay control circuit.

DTC B25F8 02 and B25F8 04

The BCM detects a short to ground or an open/high resistance in the left headlamp low beam relay control circuit.

DTC B25F9 01

The BCM detects a short to voltage in the right headlamp low beam relay control circuit.

DTC B25F9 02 and B25F9 04

The BCM detects a short to ground or an open/high resistance in the right headlamp low beam relay control circuit.

Actions Taken When the DTC Sets

The low beam headlamps will not operate.

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.

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

DTC B25F8

1. Ignition OFF, disconnect the KR49L Headlamp Low Beam Relay - Left.

2. Connect a test lamp between the control circuit terminal 2 and B+, ignition ON.

3. Verify the test lamp turns ON and OFF when commanding the High Beams ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the control circuit terminal and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • Go to next step: If less than 1 V
3. Ignition OFF.
4. Test for less than 2 Ω in the control circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K9 Body Control Module.

• Go to next step: If the test lamp turns ON and OFF

4. Test or replace the KR49L Headlamp Low Beam Relay - Left.

DTC B25F9

1. Ignition OFF, disconnect the KR49R Headlamp Low Beam Relay - Right.

2. Connect a test lamp between the control circuit terminal 2 and B+, ignition ON.

3. Verify the test lamp turns ON and OFF when commanding the High Beams ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
2. Test for less than 1 V between the control circuit terminal and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • Go to next step: If less than 1 V
3. Ignition OFF.
4. Test for less than 2 Ω in the control circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K9 Body Control Module.

• If the test lamp is always ON

1. Ignition OFF, disconnect the X5 harness connector at the K9 Body Control Module.
2. Test for infinite resistance between the control circuit terminal and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • If infinite resistance, replace the K9 Body Control Module.

• Go to next step: If the test lamp turns ON and OFF

4. Test or replace the KR49R Headlamp Low Beam Relay - Right.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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

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