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 B2575 00: Headlamp Control Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Flash to Pass Switch Signal

1

1

1

--

Headlamp Switch High Beam Signal

1

1

1

--

Headlamp Switch Headlamps ON Signal

B257A 00

1

B257A 00

--

Headlamp Switch Headlamps OFF Signal

B257A 00

1

B257A 00

--

Park Lamp Switch Park Lamps ON Signal

B257A 00

B257A 00

B257A 00

--

Headlamp High Beam Relay Control

1

1

B2580 00

--

Headlamp Low Beam Relay Control

1

1

B2575 00

--

LF High Beam Headlamp Control

1

1

1

--

LF Low Beam Headlamp Control

1

1

1

--

RF High Beam Headlamp Control

1

1

1

--

RF Low Beam Headlamp Control

1

1

1

--

LF Headlamp Ground

--

1

--

--

RF Headlamp Ground

--

1

--

--

Headlamp Switch Ground

--

1

--

--

Turn Signal/Multifunction Switch Ground

--

1

--

--

1. Headlamps Malfunction

Circuit/System Description

When the headlamp switch is placed in the headlamp position, ground is applied to the body control module (BCM) through the headlamp low beam signal circuit. The BCM then applies ground to the headlamp 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 LO BEAM fuses to the low beam headlamps.

Conditions for Running the DTC

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

Conditions for Setting the DTC

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

Action 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) Schematics

Connector End View Reference

Component Connector End Views

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, disconnect the X2 harness connector at the underhood fuse block.
  2. Connect a test lamp between B+ and the control circuit terminal A5.
  3. Command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
  4. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.
    If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. If all circuits test normal, replace the underhood fuse block.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Accessory Wiring Junction Block Replacement
    •  Control Module References for BCM replacement, setup, and programming