GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2008 🢒 Isuzu MD F-Series 🢒 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

B+ -- Left and right Headlamps

1

1

--

--

B+ -- Headlamp Hi/Lo Beam Relay Coil

1

3

--

--

B+ -- Lighting Relay Coil

1

1

--

--

B+ -- Headlamp Hi Beam Relay Coil

1

7

--

--

B+ -- Headlamp Hi Beam Relay Switch

1

7

--

--

High Beam Headlamps Control

4

3

--

--

High Beam Headlamp Indicator Control

1

7

8

--

Low Beam Headlamps Control

6

5

--

--

Headlamp Hi/Lo Beam Relay Coil Control

4

3

--

--

Lighting Relay Coil Control

6

5

--

--

Headlamp Hi Beam Relay Coil Control

8

7

--

--

Ground -- Lighting Relay

--

1

--

--

Ground -- Headlamp Hi/Lo Beam Relay

--

1, 7

--

--

Ground -- Turn Signal Multifunction Switch terminal 1

--

1

--

--

Ground -- Turn Signal Multifunction Switch terminal 5

--

5

--

--

1. Headlamps are inoperative

2. Headlamps are always ON

3. High beams headlamps are inoperative

4. High beams headlamps are always ON

5. Low beam headlamps are inoperative

6. Low beam headlamps are always ON

7. High beam indicator is inoperative

8. High beam indicator is always ON

Circuit/System Description

Battery positive voltage, from Circuit Breaker 16 located in the I/P fuse block, is supplied at all times to the high and low beam headlamps and all of the headlamp relays. With the headlamp switch in the ON position, ground from G400 is applied through the headlamp switch headlamp ON control circuit energizing the LIGHTING relay. With the relay energized, ground from G400 is applied through the switch side of the headlamp hi/lo beam relay, the switch side of the lighting relay and the headlamp control circuit illuminating the low beam headlamps. When the dimmer switch is placed in the HIGH beam position, ground from G400 is applied through the headlamp high/low beam relay control circuit energizing the HEADLAMP HI/LO BEAM relay. With the relay energized, ground from G400 is applied through the switch side of the relay and the high beam control circuits illuminating the high beam headlamps. Also with the dimmer switch in the high beam position, ground from G400 is also applied through the control circuit energizing the HEADLAMP HI BEAM relay. With the relay energized, battery voltage from Circuit Breaker 16 is applied through the high beam indicator control circuit illuminating the instrument panel cluster (IPC) 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, command the headlamps ON and OFF using turn signal multifunction switch. The headlamps should turn ON and OFF when changing between commanded states.
    2. ⇒If the headlamps are always OFF or remain always ON, refer to Headlamps Malfunction -- Low Beam.
  2. Headlamps ON, command the high beam headlamps ON and OFF using turn signal multifunction switch. The high beam headlamps and the IPC high beam indicator should turn ON and OFF when changing between commanded states.
    3. ⇒If the high beams are always OFF or remain always ON, refer to Headlamps Malfunction -- High Beam.
    ⇒If the high beam indicator does not operate as specified, refer to High Beam Indicator Malfunction.
  3. With the headlamps ON, observe the high beam headlamps while pulling and releasing the flash to pass switch. The high beam headlamps should turn ON and OFF when changing between the commanded states.
    4. ⇒If the flash to pass function is inoperative, test or replace the turn signal multifunction switch.

Circuit/System Testing

Headlamps Malfunction -- Low Beam

  1. Disconnect the harness connector at the inoperative headlamp.
  2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal C and ground.
    3. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the headlamp and disconnect the LIGHTING Relay.
  4. Test for less than 5.0 ohms between the ground circuit terminal 87 and ground.
    5. ⇒If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp HI/LO beam relay.
  5. Verify that a test lamp does not illuminate between the control circuit terminal 30 and B+.
    6. ⇒If the test lamp illuminates, test the control circuit for a short to ground.
  6. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    7. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  7. Headlamps OFF, connect a test lamp between the control circuit terminal 86 and ground. The test lamp should not illuminate.
    8. ⇒If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, test or replace the turn signal multifunction switch.
  8. Place the headlamp switch in the LOW beam position. The test lamp should illuminate.
    9. ⇒If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the turn signal multifunction switch.
  9. Connect a 10A fused jumper wire between the control circuit terminal 30 and the ground circuit terminal 87. The headlamps should illuminate.
    10. ⇒If the headlamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp.
  10. If all circuits test normal, test or replace the lighting relay.

Headlamps Malfunction -- High Beam

  1. Disconnect the harness connector at the inoperative headlamp.
  2. Ignition ON, verify that a test lamp illuminate between the appropriate B+ circuit terminals B or C and ground.
    3. ⇒ If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  3. Ignition OFF, connect the harness connector at the headlamp and disconnect the HEADLAMP HI/LO BEAM Relay.
  4. Test for less than 5.0 ohms between the ground circuit terminal 30 and ground.
    5. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    6. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  6. Headlamps OFF, connect a test lamp between the control circuit terminal 86 and ground. The test lamp should not illuminate.
    7. ⇒If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, test or replace the turn signal multifunction switch.
  7. Headlamps ON, place the dimmer switch in the HIGH beam position. The test lamp should illuminate.
    8. ⇒If the test lamp does not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the turn signal multifunction switch.
  8. Verify that a test lamp does not illuminate between the control circuit terminal 87 and B+.
    9. ⇒If the test lamp illuminates, test the control circuit for a short to ground.
  9. Connect a 10A fused jumper wire between the control circuit terminal 87 and the ground circuit terminal 30. The headlamps should illuminate.
    10. ⇒If the headlamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the headlamp.
  10. If all circuits test normal, test or replace the headlamp HI/LO beam relay.

High Beam Indicator Malfunction

  1. Ignition OFF, disconnect the HEADLAMP HI BEAM Relay.
  2. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
    3. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  4. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
    5. ⇒If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the IPC.
  5. Headlamps OFF, connect a test lamp between the control circuit terminal 86 and B+. The test lamp should not illuminate.
    6. ⇒If the test lamp illuminates, test the control circuit for a short to ground.
  6. Headlamps ON, place the dimmer switch in the HIGH beam position. The test lamp should illuminate.
    7. ⇒If the test lamp does not illuminate, test the control circuit for an open/high resistance.
  7. Install 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. The high beam indicator should illuminate.
    8. ⇒If the indicator does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the IPC.
  8. If all circuits test normal, test or replace the headlamp high beam relay.

Component Testing

Relay

  1. Ignition OFF, disconnect the appropriate relay.
  2. Test for 70-100 ohms between terminals 85 and 86.
    3. ⇒If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 85
    • 30 and 86
    • 30 and 87
    • 85 and 87
    ⇒If not the specified value, replace the appropriate relay.
  4. Test for less than 2.0 ohms of resistance between terminals 30 and 87A.
    5. ⇒If greater than the specified range, replace the appropriate relay.
  5. Install a 10A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2.0 ohms of resistance between terminals 30 and 87.
    6. ⇒If greater than the specified range, replace the appropriate relay.

Headlamp Switch

  1. Ignition OFF, disconnect the harness connector X1 at the turn signal multifunction switch.
  2. Test for infinite resistance between the ground circuit terminal 1 and the control circuit terminals listed below.
    3. • Terminal 2
    • Terminal 4
    ⇒If not the specified value, replace the turn signal multifunction switch.
  3. Test for infinite resistance between control circuit terminal 3 and the ground circuit terminal 5.
    4. ⇒If not the specified value, replace the turn signal multifunction switch.
  4. Test for less than 2.0 ohms between the control circuit terminal 2 and the ground circuit terminal 5 with the headlamp switch in the PARK position.
    5. ⇒If greater than the specified value, replace the turn signal multifunction switch.
  5. Test for less than 2.0 ohms between the control circuit terminal 4 and the ground circuit terminal 5 with the headlamp switch in the ON position.
    6. ⇒If greater than the specified value, replace the turn signal multifunction switch.
  6. Test for less than 2.0 ohms between the control circuit terminal 3 and the ground circuit terminal 5, with the dimmer switch in the high beam position.
    7. ⇒If greater than the specified value, replace the turn signal multifunction switch.
  7. Test for less than 2.0 ohms between the control circuit terminal 3 and the ground circuit terminal 5 while operating the flash to pass function, using the turn signal multifunction switch.
    8. ⇒If greater than the specified value, replace the turn signal multifunction switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Headlamp Replacement
    •  Turn Signal Multifunction Switch Replacement
    •  Relay Replacement
    •  Control Module References for IPC replacement, setup, and programming