GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2008 🢒 H3 🢒 Body Systems 🢒 Lighting 🢒 Headlamps Malfunction

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

Front Positioning Lamp Relay B+ -- European

1

1

--

--

Headlamp Relay B+

1

1

--

--

Ambient Light Sensor Signal

B2647 00

B2648 00

B2648 00

--

Flash to Pass Switch Signal

4

4

4

--

Headlamp Switch Signal

3

3

3

--

Headlamp Dimmer Switch High Beam Signal

4

4

4

--

Headlamp Off Switch Signal

3

3

3

--

Front Positioning Lamps Relay Control -- European

2

2

2

--

Headlamp Control

2

2

2

--

Headlamp High/Low Beam Relay Control

B2582 00

B2583 00

B2583 00

--

Headlamp Low Beam Relay Control

1

1

B2575 00

--

High Beam Headlamp Control

2

2

2

--

Headlamp Switch Low Reference

--

1

--

--

Front Position Lamp Ground -- European

--

2

--

--

Headlamp High/Low Beam Relay Ground

2

2

2

--

Headlamp LO BEAM Ground

1

1

1

--

Headlamp HI BEAM Ground

2

2

2

--

Turn Signal Multifunction Switch Ground

--

4,2

4,2

--

1. Headlamp Malfunction - Low Beam

2. Headlamp Malfunction - High Beam

3. Headlamp Switch Malfunction

4. Dimmer Switch Malfunction

Circuit/System Description

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the daytime running lamps (DRL) or the headlamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. When the ambient light sensor signals the BCM for DRL operation in daylight conditions, the BCM illuminates the low beam headlamps at a reduced intensity utilizing the DRL relay. The DRL will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

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 Verification
  1. Ignition ON, observe the scan tool Headlamp Off Switch parameter while cycling the headlamp switch between the Auto and Off positions. The parameter should cycle between Active while in the Off position and Inactive when released.
    2. ⇒If the parameter does not cycle between the specified values, refer to Headlamp Switch Malfunction.
  2. Observe the scan tool Headlamp On Switch parameter while cycling the headlamp switch between the Auto and Head position. The parameter should cycle between Active and Inactive.
    3. ⇒If the parameter does not cycle between the specified values, refer to Headlamp Switch Malfunction.
  3. With the headlamps ON, observe the scan tool High Beam Select Switch parameter while switching the headlamp dimmer switch between the LOW and HIGH beam positions. The parameter should cycle between Active and Inactive.
    4. ⇒If the parameter does not cycle between the specified values, refer to Dimmer Switch Malfunction.
  4. Command the Headlamps ON and OFF with a scan tool. Verify the low beam headlamps turn ON and OFF.
    5. ⇒If the low beam headlamps do not cycle between the commanded states, refer to Headlamp Malfunction - Low Beams.
  5. Command the High Beams ON and OFF with a scan tool. Verify the high beam headlamps turn ON and OFF.
    6. ⇒If the high beam headlamps do not cycle between the commanded states, refer to Headlamp Malfunction - High Beams.
  6. Command the Flash to Pass ON and OFF at the Dimmer Switch. Verify that the High Beam Headlamps turn ON and OFF between the commanded states.
    7. ⇒If the high beam headlamps do not cycle ON and OFF between the commanded states, refer to the Dimmer Switch Malfunction.
  7. Ignition ON, turn the headlamp dimmer switch to the high beam position and observe the headlamps and the IPC high beam indicator. The high beam headlamps and the high beam indicator should illuminate.
    8. ⇒If the high beam indicator does not illuminate, refer to Headlamp High Beam Indicator Malfunction

Circuit/System Testing

Headlamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp switch.
  2. Verify that a test lamp illuminates between the ground circuit terminal 3 and B+.
    3. ⇒If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool Headlamp On Switch parameter is Inactive.
    4. ⇒If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the BCM.
  4. Ignition ON, verify the scan tool Headlamp Off Switch parameter is Inactive.
    5. ⇒If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the BCM.
  5. Install a 3A fused jumper wire between the signal circuit terminal 4 and ground. Verify the scan tool Headlamp On Switch parameter is Active.
    6. ⇒If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3A fused jumper wire between the signal circuit terminal 5 and ground. Verify the scan tool Headlamp Off Switch parameter is Active.
    7. ⇒If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the headlamp switch.

Dimmer Switch Malfunction

  1. Ignition OFF, disconnect the X201 harness connector at the turn signal/multifunction switch.
  2. Test for less than 5 ohms between the ground circuit terminal B10 and ground.
    3. ⇒If more than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify the scan tool High Beam Select Switch parameter is Inactive.
    4. ⇒If not the specified value, test the signal circuit terminal A11 for a short to ground. If the circuit tests normal, replace the BCM.
  4. Ignition ON, command the flash to pass ON and OFF with the dimmer switch. The high beam headlamps should turn ON and OFF.
    5. ⇒If the high beam headlamps are always ON, test the control circuit terminal A10 for a short to ground. If the circuit tests normal, replace the BCM.
    ⇒If the high beam headlamps are always OFF, test the control circuit terminal A10 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Install a 3A fused jumper wire between the signal circuit terminal A11 and ground. Verify the scan tool High Beam Select Switch parameter is Active.
    6. ⇒If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  6. Install a 3A fused jumper wire between the signal circuit terminal A10 and ground. Verify the scan tool High Beam Select Switch parameter is Active.
    7. ⇒If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.
  7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Healdlamp Malfunction - Low Beam

  1. Ignition OFF, disconnect the HDLP relay.
  2. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
    3. ⇒If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground for an open/high resistance.
  4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    5. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground for an open/high resistance.
  5. Disconnect the harness connector at the inoperative headlamp.
  6. Test for less than 5 ohms between the ground circuit terminal A and ground.
    7. ⇒If more than the specified value, test the circuit for an open/high resistance.
  7. Test for less than 5 ohms between the ground circuit terminal A and ground.
    8. ⇒If more than the specified value, test the circuit for an open/high resistance.
  8. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the low beam headlamps are activated.
    9. ⇒If the low beam headlamps do not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the inoperative low beam headlamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Ignition ON, High Beams OFF, command the Headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    11. ⇒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.
  11. If all circuits test normal, test or replace the HDLP relay.

Headlamp Malfunction - High Beam

  1. Ignition OFF, disconnect the HI/LO BEAM relay.
  2. Test for less than 5 ohms between the ground circuit terminal and ground.
    3. ⇒If more than the specified value, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the high beam relay control circuit terminal 86 and ground.
  4. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.
    5. ⇒If the test lamp is always OFF, test the control circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the BCM.
    ⇒If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  5. Install the HI/LO BEAM relay.
  6. Disconnect the inoperative headlamp.
  7. Headlamps ON, High beams ON, test for less than 5 ohms between the ground circuit terminal C and ground.
    8. ⇒If more than the specified value, test the ground circuit for an open/high resistance.
  8. Ignition OFF, connect a test lamp between the headlamp control circuit terminal B and ground.
  9. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamps should turn ON and OFF between the commanded states.
    10. ⇒If the test lamp is always OFF, test the control circuit for a short to ground or an open high resistance. If the circuit tests normal, refer to Headlamp Malfunction - Low Beam.
    ⇒If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, refer to Headlamp Malfunction - Low Beam.
  10. If all the circuits test normal, replace the appropriate headlamp.

Headlamp High Beam Indicator Malfunction

Ignition ON, with a scan tool perform the Display Test for the instrument panel cluster (IPC) and observe the high beam indicator.

⇒If the high beam indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.
⇒If the high beam indicator illuminates during the test, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ambient Light Sensor Replacement
    •  Headlamp Switch Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Headlamp Bulb Replacement
    •  Control Module References for BCM replacement, programming, and setup