GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Uplander Ext. 🢒 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

Low Beam Headlamp Control

1

1

1

--

High Beam Headlamp Control

1

1

1

--

Headlamp Low Beam Relay Control

1

1

1

--

Headlamp High Beam Relay Control

B2580

B2580

B2580

--

Headlamp Switch Headlamps Off Signal

1

1

1

--

Headlamp Switch Headlamps On Signal

1

1

1

--

Flash to Pass Switch Signal

1

1

1

--

Headlamp Dimmer Switch High Beam Signal

1

1

1

--

Low Beam Headlamp Ground

--

1

--

--

High Beam Headlamp Ground

--

1

--

--

Headlamp Switch Ground

--

1

--

--

Turn Signal/Multifunction Switch Ground

--

1

--

--

1. Headlamps Malfunction

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 G200. 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 is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery positive voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam headlamp relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT LO and RT LO beam fuses through to the left and right low beam headlamps. 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. Observe the scan tool Flash to Pass Switch parameter while applying and releasing the flash to pass switch. The reading should toggle between ON and OFF.
    2. ⇒If the reading does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.
  2. Observe the scan tool High Beam Select switch parameter while applying and releasing the high beam select switch. The reading should toggle between ON and OFF.
    3. ⇒If the reading does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.
  3. Observe the scan tool Headlamp OFF Switch parameter while applying and releasing the headlamp OFF 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. Command the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when commanded.
    5. ⇒If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - Low Beam.
  5. Command the High Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when commanded.
    6. ⇒If the high beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - High Beam.

Circuit/System Testing

Turn Signal/Multifunction Switch Malfunction

  1. Ignition OFF, disconnect the X2 harness connector at the turn signal/multifunction switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal D.
    3. ⇒If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  3. Verify the scan tool Flash to Pass Switch parameter is OFF.
    4. ⇒If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.
  4. Verify the scan tool High Beam Select switch parameter is OFF.
    5. ⇒If not the specified value, test the signal circuit terminal E 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 A and ground. Verify the scan tool Flash to Pass Switch parameter is ON.
    6. ⇒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.
  6. Install a 3A fused jumper wire between the signal circuit terminal E and ground. Verify the scan tool High Beam Select switch parameter is ON.
    7. ⇒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.
  7. If all circuits test normal, replace the turn signal/multifunction switch.

Headlamp Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the headlamp switch.
  2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 4.
    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 does not illuminate between the headlamp ON signal circuit terminal 12 and ground.
    4. ⇒If the test lamp illuminates, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  4. Ignition ON, verify that a test lamp illuminates between the headlamp ON signal circuit terminal 12 and ground.
    5. ⇒If the test lamp does not illuminate, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Verify the scan tool Headlamp OFF Switch parameter is OFF.
    6. ⇒If not the specified value, test the signal circuit terminal 5 for a short to ground. 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 ON.
    7. ⇒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.
  7. If all circuits test normal, test or replace the headlamp 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 87 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 30 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 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 5.0 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 low beam headlamp.
  8. Connect a 20A 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. Command the Low Beam 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 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 87 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 30 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  4. 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 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 5.0 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 30 and the control circuit terminal 87. Verify the high beam headlamps are activated.
    9. ⇒If the high 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 high beam headlamp.
  9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
  10. Command the High Beam 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 high beam relay.

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.

    •  Headlamp Assembly or Headlamp Bulb and/or Cornering, Sidemarker, Park, Turn Signal Bulb Replacement
    •  Headlamp Switch Replacement
    •  Relay Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Control Module References for BCM or IPC replacement, setup, and programming