For 1990-2009 cars

### 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
--- | --- | --- | --- | ---
High Beam Relay B+ | 2 | 2 | -- | --
Low Beam Relay B+ | 1 | 1 | -- | --
Flash to Pass Switch Signal | 3 | 3 | 3 | --
Headlamp Switch High Beam Signal | 3 | 3 | 3 | --
Headlamp Switch Headlamps ON Signal | B257A 00 | 3 | 3 | --
Headlamp Switch Headlamps OFF Signal | B257A 00 | 3 | 3 | --
Headlamp High Beam Relay Control | 2 | 2 | B2580 00 | --
Headlamp Low Beam Relay Control | 1 | 1 | B2575 00 | --
LF High Beam Headlamp Control | 2 | 2 | 2 | --
LF Low Beam Headlamp Control | 1 | 1 | 1 | --
RF High Beam Headlamp Control | 2 | 2 | 2 | --
RF Low Beam Headlamp Control | 1 | 1 | 1 | --
LF Headlamp Ground | -- | 1 | -- | --
RF Headlamp Ground | -- | 1 | -- | --
Turn Signal/Multifunction Switch Ground | -- | 3 | -- | --
1. Headlamps Malfunction - Low Beam 2. Headlamps Malfunction - High Beam 3. Headlamp Switch Malfunction

### Circuit/System Description

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G201. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil is supplied with ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The underhood fuse block supplies battery voltage to the relay coil and switch circuits. The low beam headlamps operate when the BCM grounds the relay coil control circuit to the relay coil of the low beam headlamp relay. This energizes the low beam relay causing the switch contacts to close. With the switch contacts closed, battery voltage is applied to the LT LO and RT LO beam fuses through to the left and right low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LT HI BEAM and the RT HI BEAM fuses to the high beam headlamps. With the headlamp dimmer switch in the high beam position the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the 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, observe the scan tool Headlamp Switch parameter while turning the headlamp switch ON and OFF. The parameter should change between Active and Inactive.

⇒ | If the parameter does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.

2. Observe the scan tool Flash to Pass Switch parameter while applying and releasing the flash to pass switch. The parameter should change between Active and Inactive.

⇒ | If the parameter does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.

3. Observe the scan tool High Beam Select switch parameter while applying and releasing the high beam select switch. The parameter should change between Active and Inactive.

⇒ | If the parameter does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.

4. Observe the scan tool Auto Hdlp. Disable Sw. parameter while applying and releasing the automatic lamp control disable switch. The parameter should change between Active and Inactive.

⇒ | If the parameter does not change between the commanded states, refer to Turn Signal/Multifunction Switch Malfunction.

5. Command the Low Beams 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 Beams ON and OFF with a scan tool. The low 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.

### Circuit/System Testing

#### Turn Signal/Multifunction Switch Malfunction

1. Ignition OFF, disconnect the X1 and X2 harness connectors at the turn signal/multifunction switch.
2. 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. 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. Verify that a test lamp illuminates between B+ and the ground circuit terminal F.

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

5. Ignition ON, verify the scan tool Headlamp 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.

6. Verify the scan tool Auto Hdlp. Disable Sw. 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.

7. 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.

8. 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.

9. Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Headlamp 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 Auto Hdlp. Disable Sw. 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. 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 18 and B+.
3. 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 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 low beam headlamp.
6. Ignition OFF, scan tool OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 2 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 1 and ground.
8. 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 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, test or replace the appropriate 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 8 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 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 2 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 3 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, test or replace the appropriate high beam headlamp.

#### High Beam Indicator Malfunction

Ignition ON, with a scan tool perform the Display Test for the instrument panel cluster (IPC) and observe the high beam indicator.

⇒ | If the high beam indicator illuminates during the test, replace the BCM.

⇒ | If the high beam indicator does not illuminate during the test or remains illuminated at all times, replace the IPC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Replacement

• | Headlamp Bulb Replacement

• | Underhood Electrical Center or Junction Block Replacement

• | Turn Signal Multifunction Switch Replacement

• | Control Module References for BCM replacement, setup and programming