GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 XLR 🢒 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

Flash to Pass Switch Signal

1

1

1

--

Headlamp Switch High Beam Signal

1

1

1

--

Headlamp Switch Headlamps On Signal

1

1

1

--

Headlamp Switch Headlamps Off Signal

1

1

1

--

Headlamp High Beam Relay Control

B2580 06

B2580 06

B2580 01

--

Headlamp Low Beam Relay Control

2

2

2

--

LF High Beam Headlamp Control

3

3

3

--

LF Low Beam Headlamp Control

2

2

2

--

RF High Beam Headlamp Control

3

3

3

--

RF Low Beam Headlamp Control

2

2

2

--

LF Headlamp Ground

--

2, 3

2, 3

--

RF Headlamp Ground

--

2, 3

2, 3

--

Turn Signal/Multifunction Switch Ground

--

1

1

--

1. Headlamp Switch Malfunction

2. Headlamps Malfunction - Low Beam

3. Headlamps Malfunction - High Beam

Circuit/System Description

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G201. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery voltage to both relay switch circuits. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the high beam headlamps. With the headlamp dimmer switch in the high beam position the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.

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 turning the headlamp switch ON and OFF. The reading should toggle between Off and On.
    2. ⇒If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.
  2. Observe the scan tool Flash To Pass Switch parameter while applying and releasing the flash to pass switch. The reading should toggle between Active and Inactive.
    3. ⇒If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.
  3. Observe the scan tool High Beam Select switch parameter while applying and releasing the high beam select switch. The reading should toggle between Active and Inactive.
    4. ⇒If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.
  4. Observe the scan tool Headlamp On Switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between Active and Inactive.
    5. ⇒If the reading does not change between the commanded states, refer to Headlamp Switch Malfunction.

Circuit/System Testing

Headlamp Switch Malfunction

  1. Ignition OFF, disconnect the X2 and X3 harness connectors at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal K.
    3. ⇒If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal B.
    4. ⇒If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  4. Ignition ON, verify the scan tool Headlamp Off Switch parameter is Off.
    5. ⇒If not the specified value, test the signal circuit terminal N for a short to ground. If the circuit tests normal, replace the BCM.
  5. Verify the scan tool Flash To Pass Switch parameter is INACTIVE.
    6. ⇒If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.
  6. Verify the scan tool High Beam Select Switch parameter is Inactive.
    7. ⇒If not the specified value, test the signal circuit terminal E for a short to ground. If the circuit tests normal, replace the BCM.
  7. Verify the scan tool Headlamp On Switch parameter is Inactive.
    8. ⇒If not the specified value, test the signal circuit terminal L for a short to ground. If the circuit tests normal, replace the BCM.
  8. Install a 3A fused jumper wire between the signal circuit terminal N and ground. Verify the scan tool Headlamp Off Switch parameter is On.
    9. ⇒If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  9. Install a 3A fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Flash To Pass Switch parameter is Active.
    10. ⇒If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  10. Install a 3A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool High Beam Select Switch parameter is Active.
    11. ⇒If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  11. Install a 3A fused jumper wire between the signal circuit terminal L and ground. Verify the scan tool Headlamp ON Switch parameter is Active.
    12. ⇒If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
  12. If all circuits test normal, test or replace the turn signal/multifunction switch.

Headlamps Malfunction -- Low Beam

  1. Ignition OFF, disconnect the low beam relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal M3 and ground.
    3. ⇒If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the B+ circuit terminal K3 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal M3 for a short to ground. If the circuit tests normal, test or replace the low beam relay.
  4. Verify that a test lamp illuminates between the B+ circuit terminal K2 and ground.
    5. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Disconnect the harness connector at the inoperative low beam headlamp.
  6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 3 and ground.
    7. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the inoperative low beam headlamp.
  8. Connect a 40A fused jumper wire between the B+ circuit terminal K2 and the control circuit terminal M3. Verify the low beam headlamps are activated.
    9. ⇒If the low beam headlamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative low beam headlamp.
  9. Connect a test lamp between the B+ circuit terminal K3 and the control circuit terminal M2.
  10. Command the low beam headlamps ON and OFF with the headlamp switch. 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 low beam relay.

Headlamps Malfunction -- High Beam

  1. Ignition OFF, disconnect the high beam relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal H2 and ground.
    3. ⇒If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the B+ circuit terminal F2 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal H2 for a short to ground. If the circuit tests normal, test or replace the high beam relay.
  4. Verify that a test lamp illuminates between the B+ circuit terminal F1 and ground.
    5. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  5. Disconnect the harness connector at the inoperative high beam headlamp.
  6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal B and ground.
    7. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the inoperative high beam headlamp.
  8. Connect a 20A fused jumper wire between the B+ circuit terminal F1 and the control circuit terminal H2. Verify the high beam headlamps are activated.
    9. ⇒If the high beam headlamps do not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative high beam headlamp.
  9. Connect a test lamp between the B+ circuit terminal F2 and the control circuit terminal H1.
  10. Command the high beam headlamps ON and OFF with the high beam switch. 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 high beam relay.

High Beam Indicator Malfunction

Ignition ON, with a scan tool perform the Display Test for the IPC and observe the high beam indicator.

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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  High Intensity Discharge Headlamp Starter/Arc Tube Replacement
    •  High Intensity Discharge Headlamp Ballast Replacement
    •  Underhood Electrical Center or Junction Block Replacement
    •  Relay Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for BCM or IPC replacement, setup, and programming