GM Service Manual Online
For 1990-2009 cars only

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 Descriptor

DTC B2600 00: Daytime Running Lamp Control Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

DRL Relay Control Circuit

1

2

B2600 00

--

  1. Daytime Running Lamps (DRL) Always On
  2. Daytime Running Lamps (DRL) Inoperative

Circuit/System Description

The daytime running lamps (DRL) are controlled by the body control module (BCM). The BCM grounds the DRL or DRL  2 relay control circuit in order to energize the DRL relay coil. The DRL or DRL 2 relay then sends voltage to the dedicated DRL or low beam headlamps.

Conditions for Running the DTCs

    • The headlamp switch is OFF.
    • The park brake is unapplied.
    • The engine is running.

Conditions for Setting the DTC

The DRL relay control circuit is shorted to voltage.

Action Taken When the DTC Sets

The BCM turns off the DRL relay control for the remainder of the ignition cycle.

Conditions for Clearing the DTC

    • The conditions for setting the DTC are no longer present.
    • A history DTC clears after 100 malfunction-free ignition cycles.
    • The BCM receives the clear code command from the scan tool.

Reference Information

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Output Controls
    •  Scan Tool Data List
    •  Scan Tool Data Definitions

Circuit/System Verification

Block the drive wheels. Carefully supply sufficient light to simulate daylight conditions to the ambient light sensor. With the engine running, headlamp switch in AUTO, and the park brake released, the DRL should illuminate.

Circuit/System Testing

  1. Ignition OFF, disconnect the BCM connector X4 or X7.
  2. Ignition ON, test for voltage at the BCM harness connector terminal 23 or 8.
  3. If voltage is present, test the control circuit for a short to voltage. If all circuits/connections test normal, replace the I/P fuse block.
    If voltage is not present, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Underhood Electrical Center or Junction Block Replacement
    •  Control Module References for BCM replacement, setup, and programming