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Headlamps Malfunction




Headlamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit/System Description

The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: OFF, AUTOMATIC LIGHT, PARKING LIGHT, and LOW BEAM. The default headlamp switch position is AUTOMATIC LIGHT, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The OFF portion of the headlamp switch is a momentary switch which overrides the automatic headlamp and will turn OFF the vehicle headlamps. When in the OFF position, the headlamp switch grounds the headlamp switch headlamps OFF signal circuit, prompting the BCM to turn OFF the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The LOW BEAM position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the LOW BEAM position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.

The headlamp high beams are controlled through the flash to pass switch and the high beam select, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The high beam select switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the high beam select switch is in the high beam position, the high beam select switch signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.

The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM supplies an B+ to the headlamp low beams. This B+ then, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the headlamp high beam relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the left high beam and right high beam fuses, illuminating the high beam headlamps.

Reference Information
Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, observe the scan tool Headlamps On Switch, Park Lamps Switch and Automatic Headlamps Disable Switch parameters while selecting the headlamp control switch between the Off, park lamps and headlamps settings. Each parameter should be Inactive and change to Active as each setting is selected.

• If a value does not change between the commanded states, refer to Headlamp Switch Malfunction.

2. Observe the scan tool High Beam Select Switch parameter while selecting the S78 turn signal/multifunction switch between the high beam position and the low beam position. The value should change between Inactive and Active while selecting between the two positions.

• If a value does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.

3. Observe the scan tool Headlamps Flash Switch parameter while pulling and releasing the S78 turn signal/multifunction switch. The value should be Inactive and change to Active as the switch is pulled and released

• If a value does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.

4. Command the Low Beam Lamps ON and OFF with a scan tool. The E4G headlamp-left low beam and the E4H headlamp-right low beam should turn ON and OFF when changing between the commanded states.

• If the E4G headlamp-left low beam and the E4H headlamp-right low beam are always ON or always OFF, refer to Low Beam Headlamps Malfunction.

5. Command the High Beams ON and OFF with a scan tool. The E4E headlamp-left high beam and the E4F right high beam should turn ON and OFF when changing between the commanded states.

• If the E4E headlamp-left high beam or the E4F right high beam low beam is always OFF, refer to High Beam Headlamps Inoperative
• If both high beam headlamps are always ON or always OFF, refer to High Beam Command Malfunction.

Circuit/System Testing

Headlamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the S30 headlamp switch.
2. Ignition OFF, test for less than 30 ohm between the ground circuit terminal 6 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Park Lamps Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the K9 BCM.

4. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 6. Verify the scan tool Park Lamps Switch is Active.

• 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 K9 BCM.

5. Verify the scan tool Headlamps On Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K9 BCM.

6. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 6. Verify the scan tool Headlamps On Switch is Active.

• 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 K9 BCM.

7. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the K9 BCM.

8. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the ground circuit terminal 6. Verify the scan tool Automatic Headlamps Disable Switch is Active.

• 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 K9 BCM.

9. If all circuits test normal, test or replace the S30 headlamp switch.

Turn Signal/Multifunction Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the S78 turn signal/multifunction switch.
2. Ignition OFF, test for less than 30 ohm between the ground circuit terminal 3 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Headlamps Flash Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K9 BCM.

4. Install a 3 A fused jumper wire between the signal circuit terminal 4 and ground. Verify the scan tool Headlamps Flash Switch parameter is Active.

• 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 K9 BCM.

5. Verify the scan tool High Beam Select Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the K9 BCM.

6. Install a 3 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool High Beam Select Switch parameter is Active.

• 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 K9 BCM.

7. If all circuits test normal, test or replace the S78 turn signal/multifunction switch.

Low Beam Headlamps Malfunction
1. Ignition OFF, disconnect the harness X1 harness connector at the K9 BCM.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminals listed below and ground:

* B+ circuit terminal 2
* B+ circuit terminal 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 X1 harness connector at the K9 BCM.
4. Disconnect the harness connector at the appropriate E4 headlamp-low beam.
5. Test for less than 30 ohm between the ground circuit terminal B and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

6. Connect a test lamp between the control circuit terminal A and ground.
7. Ignition ON, command the low beam lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF while changing between the commanded states.

• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K9 BCM.
• 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, replace the K9 BCM

8. If all circuits test normal, replace the headlamp bulb.

High Beam Headlamps Inoperative
1. Ignition OFF, disconnect the harness connector at the appropriate E4 Headlamp- high beam.
2. Test for less than 30 ohm between the ground circuit terminal B and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Connect a test lamp between the control circuit terminal A and ground.
4. Ignition ON, command the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• 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, replace the X50A underhood fuse block.
• If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the X50A underhood fuse block.

5. If all circuits test normal, test or replace the bulb or the E4 Headlamp- high beam

High Beam Command Malfunction
1. Ignition OFF, disconnect the X2 harness connector at the X50A underhood fuse block.
2. Connect a test lamp between the control circuit terminal 58 and B+.
3. Ignition ON, command the High Beam Lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

• 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 K9 BCM.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 BCM

4. Ignition OFF, connect the X2 harness connector and disconnect the X1 harness connector at the X50A underhood fuse block.
5. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminals listed below and ground.

* Control terminal 13
* Control terminal 14

• If the test lamp is always ON, test the control circuit for a short to voltage.

6. If all circuits test normal, replace the X50A underhood fuse block.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Fuse Block Replacement (Fuse Block Replacement)
* Headlamp Switch Replacement (Service and Repair)
* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Headlamp Replacement (Headlamp Replacement)
* Headlamp Bulb Replacement (TT2) (Headlamp Bulb Replacement (TT2))Headlamp Bulb Replacement (TT4 Low Beam) (Headlamp Bulb Replacement (TT4 Low Beam))Headlamp Bulb Replacement (TT4 High Beam) (Headlamp Bulb Replacement (TT4 High Beam))
* Control Module References (Programming and Relearning) for BCM replacement, programming and setup

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