Circuit/System Testing

Headlamp Switch Malfunction

1. Ignition OFF, disconnect the X1 and X2 harness connectors at the turn signal/multifunction switch.
2. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal 1.
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
3. Ignition OFF, verify that a test lamp illuminates between B+ and the ground circuit terminal B.
   • If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
4. 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 BCM.
5. Verify the scan tool Headlamp Off Switch parameter is Inactive.
   • If not the specified value, test the signal circuit terminal 4 for short to ground. If the circuit tests normal, replace the BCM.
6. Verify the scan tool Flash to Pass Switch parameter is Inactive.
   • If not the specified value, test the signal circuit terminal C for a short to ground. If the circuit tests normal, replace the BCM.
7. Verify the scan tool High Beam Select Switch parameter is Inactive.
   • If not the specified value, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the BCM.
8. Verify the scan tool Low Beam Relay Command parameter is Off.
   • If not the specified value, test the signal circuit terminal F for a short to voltage. If the circuit tests normal, replace the BCM.
9. Install a 3A 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 BCM.
10. Install a 3A fused jumper wire between the signal circuit terminal 4 and ground. Verify the scan tool Headlamp Off 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.
11. Install a 3A fused jumper wire between the signal circuit terminal C 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 an open/high resistance. If the circuit tests normal, replace the BCM.
12. Install a 3A fused jumper wire between the signal circuit terminal D 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 an open/high resistance. If the circuit tests normal, replace the BCM.
13. Install a 10A fused jumper wire between the signal circuit terminal F and ground. Verify the scan tool Low Beam Relay Command parameter is On.
    • If not 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.
14. If all circuits test normal, test or replace the turn signal/multifunction switch.

Headlamps Malfunction - Low Beam

1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal C2 and B+.
3. Command the low beam headlamps ON and OFF with the headlamp switch. 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 turn signal/multifunction switch.
   • 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 turn signal/multifunction switch.
4. Ignition OFF, connect the X2 harness connector at the underhood fuse block.
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 ohms between the ground circuit terminal B and ground.
   • If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect a test lamp between the control circuit terminal A and ground.
8. Command the low beam headlamps ON and OFF with the headlamp switch. 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 underhood fuse block.
   • If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
   • If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.
9. If all circuits test normal, replace the inoperative low beam headlamp.

Headlamps Malfunction - High Beam

1. Ignition OFF, disconnect the X2 harness connector at the underhood fuse block.
2. Connect a test lamp between the control circuit terminal A2 and B+.
3. 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. Ignition OFF, connect the X2 harness connector at the underhood fuse block.
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 ohms between the ground circuit terminal B and ground.
   • If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect a test lamp between the control circuit terminal C and ground.
8. 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 voltage. If the circuit tests normal, replace the underhood fuse block.
   • If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
   • If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, replace the underhood fuse block.
9. If all circuits test normal, replace the inoperative high beam headlamp.

Automatic Lamp Control (ALC) Malfunction

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 10 ohms between the low reference circuit terminal B and ground.
   • If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
3. If all circuits test normal, replace the ambient light sensor.