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Headlamps Malfunction




Headlamps Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle
* Review Strategy Based Diagnosis Strategy Based Diagnosis
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions

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 switch, 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 signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.

Reference Information
Schematic Reference

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

Component Connector End Views Hybrid/EV Battery Pack X1 A4
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 Control Module References

Circuit/System Verification

1. Ignition ON, observe the scan tool Headlamp On Switch parameter while turning the headlamp switch ON and OFF. The reading should toggle between Active and Inactive.

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

2. Observe the scan tool Automatic Headlamp Disable Switch parameter while applying and releasing the automatic lamp control disable switch. The reading should toggle between Active and Inactive.

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

3. Observe the scan tool Headlamps Flash Switch parameter while applying and releasing the flash to pass switch. The reading should toggle between Active and Inactive.

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

4. 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.

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

5. Command the Low Beam Relay Command ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when commanded.

• If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - Low Beam.

6. Command the High Beam Command ON and OFF with a scan tool. The high beam headlamps should turn ON and OFF when commanded.

• If the high beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction - High Beam.

7. Command the All Indicators Test ON and OFF with a scan tool. The high beam indicator should turn ON and OFF when changing between the commanded states.

• If the high beam indicator illuminates during the test, replace the K9 BCM.
• If the high beam indicator does not illuminate during the test or remains illuminated at all times, replace the P16 instrument cluster.

Circuit/System Testing

Headlamp Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the S78 turn signal/multifunction switch.
2. Ignition OFF, test for less than 5 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 Headlamp On Switch parameter is Inactive.

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

4. Verify the scan tool Automatic Headlamp Disable Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 9 for short to ground. If the circuit tests normal, replace the K9 BCM.

5. Install a 3 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Headlamp On 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.

6. Install a 3 A fused jumper wire between the signal circuit terminal 9 and ground. Verify the scan tool Automatic Headlamp Disable 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.

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

Turn Signal/Multifunction Switch Malfunction
1. Ignition OFF, disconnect the harness connector at the turn S78 turn signal/multifunction switch.
2. Ignition OFF, test for less than 5 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 Headlamps Flash Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 12 for a short to ground. If the circuit tests normal, replace the K9 BCM.

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

• If not the specified value, test the signal circuit terminal 11 for a short to ground. If the circuit tests normal, replace the K9 BCM.

5. Install a 3 A fused jumper wire between the signal circuit terminal 12 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 and open/high resistance. If the circuit tests normal, replace the K9 BCM.

6. Install a 3 A fused jumper wire between the signal circuit terminal 11 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.

Headlamps Malfunction - Low Beam
1. Ignition OFF, disconnect the harness connector at the appropriate E4 low beam headlamp.
2. Ignition OFF, scan tool disconnected, exterior lamps OFF, test for less than 5 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. Command the Low Beam Relay Command 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 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 open/high resistance. If the circuit tests normal, replace the K9 BCM.

5. If all circuits test normal, test or replace the E4 low beam headlamp.

Headlamps Malfunction - High Beam
1. Ignition OFF, disconnect the KR48 headlamp high beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 4 and ground.

• 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 1 and ground.

• 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 3 and ground.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

5. Disconnect the harness connector at the appropriate E13 headlamp.
6. Test for less than 5 ohm between the ground circuit terminal 4 and ground.

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

7. Connect the harness connector at the E13 headlamp.
8. Connect a 10 A fused jumper wire between the B+ circuit terminal 3 and the control circuit terminal 4. Verify the M28 high beam solenoid actuator is activated.

• If the M28 high beam solenoid actuator is not activated and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the M28 high beam solenoid actuator.
• If the M28 high beam solenoid actuator is not activated and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the M28 high beam solenoid actuator.

9. Connect a test lamp between the B+ circuit terminal 1 and the control circuit terminal 2.
10. Command the High Beam Command 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 ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K9 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 K9 BCM.

11. If all circuits test normal, test or replace the KR48 headlamp high beam relay.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests

* Turn Signal Multifunction Switch Replacement Turn Signal Multifunction Switch Replacement
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Headlamp Replacement Removal and Replacement
* Headlamp Bulb Replacement Service and Repair
* Control Module References Control Module References

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