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, Auto, Park, and Headlamps. The default headlamp switch position is Auto, 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 headlamps 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 Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Headlamp 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 headlamp dimmer 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 headlamp dimmer 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 headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam 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 grounds the headlamp low beam relay control circuit. This energizes the coil in the LOW BEAM PCB relay, causing the relay switch to close. This then applies B+ to both low beam headlamps through the LT LO BEAM and RT LO BEAM fuses, 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 HIGH BEAM PCB relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the LT HI BEAM and RT HI BEAM fuses, illuminating the high beam headlamps.

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Lighting Systems Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool Auto Hdlp. Disable Sw. parameter while cycling the headlamp switch between the Auto and Off positions. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Headlamp Switch Circuit Test.

2. Turn the headlamp switch to the PARK position and observe the scan tool Headlamp Switch parameter. The reading should be Inactive.

⇒	If not the specified value, refer to Headlamp Switch Circuit Test.

3. Observe the scan tool Headlamp Switch parameter while cycling the headlamp switch between the Auto and Head position. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Headlamp Switch Circuit Test.

4. With the headlamps ON, observe the scan tool Flash to Pass Switch parameter while pulling and releasing the flash to pass switch. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Turn Signal/Multifunction Switch Circuit Test.

5. With the headlamps ON, observe the scan tool High Beam Select Switch parameter while switching the headlamp dimmer switch between the low and high beam positions. The reading should change between Active and Inactive.

⇒	If the reading does not change between the specified values, refer to Turn Signal/Multifunction Switch Circuit Test.

6. Ignition ON and headlamps OFF, with a test lamp connected to ground, probe each of the test points on the LT LO BEAM fuse while commanding the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF at one or both of the fuse test points.

⇒	If the test lamp does not turn ON and OFF when changing between the commanded states, refer to Low Beam Relay Test.

7. Observe the low beam headlamps while commanding the Low Beams ON and OFF with a scan tool. The low beam headlamps should turn ON and OFF when changing between the commanded states.

⇒	If the low beam headlamps do not turn ON and OFF when changing between the commanded states, refer to Low Beam Headlamp Circuit Test.

8. Ignition ON and headlamps OFF, with a test lamp connected to ground, probe each of the test points on the LT HI BEAM fuse while commanding the High Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF at one or both of the fuse test points.

⇒	If the test lamp does not turn ON and OFF when changing between the commanded states, refer to High Beam Relay Test.

9. Observe the high beam headlamps while commanding the High Beams ON and OFF with a scan tool. The high beam headlamps should turn ON and OFF when changing between the commanded states.

⇒	If the high beam headlamps do not turn ON and OFF when changing between the commanded states, refer to High Beam Headlamp Circuit Test.

10. With the high beam headlamps ON, the instrument panel cluster (IPC) high beam indicator should be illuminated.

⇒	If the high beam indicator is not illuminated, refer to High Beam Indicator Malfunction.

Headlamp Switch Circuit Test

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, test for B+ between the signal circuit terminals listed below and ground.

•	Headlamp switch headlamps ON signal terminal 1

•	Park lamp switch ON signal terminal 2

•	Headlamp switch OFF signal terminal 3

⇒	If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the park lamp ON signal circuit terminal 2 and ground. Verify the scan tool Parklamp 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 BCM.

5. Install 3A fused jumper wires between both signal circuit terminals listed below and ground. Verify the scan tool Headlamp Switch parameter is Active.

•	Headlamps ON terminal 1

•	Park lamp signal terminal 2

⇒	If not the specified value, test the signal circuit terminal 1 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

6. Remove the jumper wires from terminal 1 and terminal 2. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto Hdlp. Disable Sw. 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 BCM.

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

Turn Signal/Multifunction Switch Circuit Test

1. Ignition OFF, disconnect the C2 harness connector at the turn signal/multifunction switch.
2. Verify that a test lamp illuminates between the ground circuit terminal D and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

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

⇒	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 Inactive.

⇒	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 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 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 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 BCM.

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

Low Beam Relay Test

1. Ignition OFF, disconnect the C2 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal A5 and B+.
3. Ignition ON, command the Low 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 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.

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

Low Beam Headlamp Circuit Test

1. Ignition OFF, disconnect the harness connector at the inoperative low beam headlamp.
2. Test for less than 5.0 ohms 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 supply voltage circuit terminal A and ground.
4. Ignition ON, command the Low 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 ON, test the supply voltage circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

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

High Beam Relay Test

1. Ignition OFF, disconnect the C2 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal C6 and B+.
3. 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 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.

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

High Beam Headlamp Circuit Test

1. Ignition OFF, disconnect the harness connector at the inoperative high beam headlamp.
2. Test for less than 5.0 ohms 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 supply voltage 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 ON, test the supply voltage circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.

⇒	If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.

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

High Beam Indicator Malfunction

Ignition ON, perform the IPC Display Test with a scan tool. The IPC high beam indicator should illuminate.

Headlamp Switch

Important: If the switch tests open in any switch position other than Auto, test the switch signal circuits for a short to voltage before replacing the switch.

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal terminal 1 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

3. Test for less than 2.0 ohms between the signal terminal 1 and the ground terminal 8 with the switch in the Headlamp position

⇒	If greater than the specified value, replace the headlamp switch.

4. Test for infinite resistance between the signal terminal 2 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

5. Test for less than 2.0 ohms between the signal terminal 2 and the ground terminal 8 with the switch in the Park position.

⇒	If greater than the specified value, replace the headlamp switch.

6. Test for infinite resistance between the signal terminal 3 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

7. Test for less than 2.0 ohms between the signal terminal 3 and the ground terminal 8 with the switch in the Off position.

⇒	If greater than the specified value, replace the headlamp switch.

Turn Signal/Multifunction Switch

1. Ignition OFF, disconnect the harness connector C2 at the turn signal/multifunction switch.
2. Test for infinite resistance between the signal terminal A and the ground terminal D with the flash to pass switch in the open position.

⇒	If not the specified value, replace the turn signal/multifunction switch.

3. Test for infinite resistance between the signal terminal E and the ground terminal D with the headlamp dimmer switch in the low beam position.

⇒	If not the specified value, replace the turn signal/multifunction switch.

Important: If the switch tests open in any switch position other than Off, test the switch signal circuits for a short to voltage before replacing the switch.

4. Test for less than 2.0 ohms of resistance between the signal terminal A and the ground terminal D with the flash to pass switch in the closed position.

⇒	If greater than the specified value, replace the turn signal/multifunction switch.

5. Test for less than 2.0 ohms of resistance between the signal terminal E and the ground terminal D with the headlamp dimmer switch in the high beam position.

⇒	If greater than the specified value, replace the turn signal/multifunction switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.