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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Flash to Pass Switch Signal

1

5

5

--

Headlamp High Beam Relay Control

B2580 06

B2580 06

B2580 01

--

Headlamp Dimmer Switch High Beam Signal

1

2

2

--

Headlamp Switch Headlamps On Signal

1

4

4

--

Headlamp Switch Headlamps Off Signal

4

1

1

--

Headlamp Switch Signal

1

4

4

--

Low Beam Relay Control

1

3

3

--

LF High Beam Headlamp Voltage Supply

2

2

1

--

LF Low Beam Headlamp Voltage Supply

3

3

1

--

RF High Beam Headlamp Voltage Supply

2

2

1

--

RF Low Beam Headlamp Voltage Supply

3

3

1

--

LF Headlamp Ground

--

4

4

--

RF Headlamp Ground

--

4

4

--

Turn Signal/Multifunction Switch Ground

--

4

4

--

1. Headlamps Always On - Low or High Beams

2. Headlamps Inoperative - High Beams

3. Headlamps Inoperative - Low Beams

4. Headlamps Inoperative - Low and High Beams

5. Headlamps Inoperative - Flash to Pass

Circuit/System Description

When the turn signal/multifunction switch is placed in the headlamps high beam or flash to pass (FTP) position, ground is applied to the body control module (BCM) through the headlamp high beam signal circuit or the flash to pass switch signal circuit. The BCM then applies ground to the headlamp high beam relay control circuit which energizes the high beam relay, applying battery voltage to the high beam headlamps.

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 Testing

  1. Ignition OFF, disconnect the C2 harness connector at the turn signal/multifunction switch.
  2. Connect a 3-amp fused jumper between the flash to pass switch signal circuit and ground at the turn signal/multifunction switch harness connector.
  3. Ignition ON, install a scan tool and observe the Flash to Pass Switch parameter. The scan tool parameter should display Active.
  4. If the scan tool indicates the Flash to Pass Switch parameter is Inactive, repair the flash to pass switch signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Verify that a test lamp illuminates between battery voltage and the flash to pass switch ground circuit at the turn signal/multifunction switch harness connector.
  6. If the test lamp does not illuminate, repair the flash to pass switch ground circuit for an open/high resistance.
  7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for BCM replacement, setup, and programming