Buick Regal: DTC B2600 or B2605

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 B2600 01

Left Daytime Running Lamps Control Circuit short to Battery

DTC B2600 02

Left Daytime Running Lamps Control Circuit Short to Ground

DTC B2600 04

Left Daytime Running Lamps Control Circuit Open

DTC B2605 01

Right Daytime Running Lamps Control Circuit short to Battery

DTC B2605 02

Right Daytime Running Lamps Control Circuit Short to Ground

DTC B2605 04

Right Daytime Running Lamps Control Circuit Open

Diagnostic Fault Information

1. Headlamps Malfunction
2. Daytime Running Lamps Malfunction

Circuit/System Description

The ambient light sensor is used to monitor outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor. Depending on outside lighting conditions, the ambient light sensor provides a voltage signal to the BCM that will vary between 0.2 and 4.9 volts. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic headlamp system control when the headlamp switch is in the AUTO position. In daylight conditions, the BCM will command the DRLs. Any function or condition that turns on the headlamps will cancel DRL operation.

Conditions for Running the DTC

• Battery voltage must be between 9-16 V.
• Headlamp switch in AUTO position.

Conditions for Setting the DTC

DTC B2600 01

The BCM detects a short to voltage in the left DRL control circuit.

DTC B2600 02

The BCM detects a short to ground in the left DRL control circuit.

DTC B2600 04

The BCM detects an open/high resistance in the left DRL control circuit.

DTC B2605 01

The BCM detects a short to voltage in the right DRL control circuit.

DTC B2605 02

The BCM detects a short to ground in the right DRL control circuit.

DTC B2605 04

The BCM detects an open/high resistance in the right DRL control circuit.

Actions Taken When the DTC Sets

• When DTC B2600 sets, the left DRL will be inoperative.
• When DTC B2605 sets, the right DRL will be 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.

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.

2. Test for less than 5 Ω between the ground circuit terminal 1 and ground.

• If 5 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 5 Ω

3. Connect a test lamp between the control circuit terminal 4 and ground, ignition ON.

4. Verify the test lamp turns ON and OFF when commanding the appropriate Front Park Lamp/Daytime Running Lamp ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the X4 harness connector at the K9 body control module.
2. Test for infinite resistance between the control circuit 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 K9 body control module.

• If the test lamp is always ON

1. Ignition OFF, disconnect the X4 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.
   • If less than 1 V, replace the K9 body control module.

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

5. Test or replace the appropriate E13 headlamp.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Headlamp Replacement
• Control Module References for BCM replacement, programming, and setup

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