Buick Regal: DTC B25FA or B25FB

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 B25FA 03

Left Headlamp Leveling Control Module Supply Circuit Low Voltage

DTC B25FA 07

Left Headlamp Leveling Control Module Supply Circuit High Voltage

DTC B25FB 03

Right Headlamp Leveling Control Module Supply Circuit Low Voltage

DTC B25FB 07

Right Headlamp Leveling Control Module Supply Circuit High Voltage

Diagnostic Fault Information

1. Headlamp Leveling Malfunction

Circuit/System Description

The automatic headlamp leveling system automatically maintains the vertical alignment of the headlamps when the vehicle load and driving conditions change. The vehicle is equipped with suspension height sensors located on the left front and left rear suspensions. Each sensor receives a 5 V reference, signal, and low reference circuits from the headlamp control module. The headlamp control module receives inputs from the front and rear suspension height sensors to determine vehicle pitch. The headlamp control module calculates the difference in vehicle pitch and sends a serial data message to both headlamp leveling control modules located in each headlamp assembly. The headlamp leveling control modules responds by driving their respective headlamp leveling actuators to the position commanded by the headlamp control module.

Conditions for Running the DTC

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

Conditions for Setting the DTC

DTC B25FA 03

The headlamp control module detects a low voltage condition in the headlamp leveling control module - left B+ circuit.

DTC B25FA 07

The headlamp control module detects a high voltage condition in the headlamp leveling control module - left B+ circuit.

DTC B25FB 03

The headlamp control module detects a low voltage condition in the headlamp leveling control module - right B+ circuit.

DTC B25FB 07

The headlamp control module detects a high voltage condition in the headlamp leveling control module - right B+ circuit.

Actions Taken When the DTC Sets

• Advanced front lighting and headlamp leveling are disabled.
• The driver information center will display "Advanced Front Lighting System Fault" and "Headlamp Leveling Malfunction".

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

No parts within the headlamp assemblies are serviceable so complete headlamp assembly replacement is necessary. When replacing a headlamp assembly, the following control modules located on each headlamp assembly should be reused.

• K189L Headlamp/Cornering Lamp Control Module - Left
• K189R Headlamp/Cornering Lamp Control Module - Right
• K28L Headlamp Leveling Control Module - Left
• K28R Headlamp Leveling Control Module - Right

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 OFF, exterior lamps OFF, disconnect the harness connector at the appropriate E13 Headlamp Assembly. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 10 Ω between the ground circuit terminal 2 and ground.

• If 10 Ω or greater

1. Ignition OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, repair the open/high resistance in the ground connection.

• Go to next step: If less than 10 Ω

3. Ignition ON.

4. Verify a test lamp illuminates between the B+ circuit terminal 6 and ground.

• If the test lamp does not illuminate

1. Ignition OFF, disconnect the X5 harness connector at the X50A Fuse Block - Underhood.
2. Test for infinite resistance between the B+ circuit terminal 6 and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. 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 X50A Fuse Block - Underhood.

• Go to next step: If the test lamp illuminates

5. Replace the E13 Headlamp Assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Headlamp Replacement
• Engine Wiring Harness Fuse Block Bracket Replacement
• Control Module References for Headlamp Control Module replacement, programming, and setup

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