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
--- | --- | --- | --- | ---
Flash to Pass Switch Signal | 1 | 1 | 1 | --
Headlamp Switch High Beam Signal | 1 | 1 | 1 | --
Headlamp Switch Headlamps On Signal | 1 | 1 | 1 | --
Headlamp Switch Headlamps Off Signal | 1 | 1 | 1 | --
Headlamp High Beam Relay Control | B2580 06 | B2580 06 | B2580 01 | --
Headlamp Low Beam Relay Control | 2 | 2 | 2 | --
LF High Beam Headlamp Control | 3 | 3 | 3 | --
LF Low Beam Headlamp Control | 2 | 2 | 2 | --
RF High Beam Headlamp Control | 3 | 3 | 3 | --
RF Low Beam Headlamp Control | 2 | 2 | 2 | --
LF Headlamp Ground | -- | 2, 3 | -- | --
RF Headlamp Ground | -- | 2, 3 | -- | --
Turn Signal/Multifunction Switch Ground | -- | 1 | -- | --
1. Headlamp Switch Malfunction 2. Headlamps Malfunction - Low Beam 3. Headlamps Malfunction - High Beam

### Circuit/System Description

With the headlamp switch in the HEAD position, the headlamp switch headlamp ON signal circuit is grounded through the turn signal/multifunction switch at G300. In response to this input, the body control module (BCM) provides ground to either the headlamp low beam relay control circuit through the headlamp switch signal circuit or the headlamp high beam relay control circuit. The position of the headlamp dimmer switch determines which relay coil has ground. The BCM supplies ground to the relay coil circuits, if the headlamps are necessary. The LO BEAM and HI BEAM relays are supplied with battery positive voltage at there coil and switch input circuits. When the low beam relay coil is energized, current flows through the LH LOW and the RH LOW fuses to the low beam headlamps. When the headlamp high beam relay coil is energized, current flows through the LH HIGH and the RH HIGH fuses to the high beam headlamps. The headlights may be switched to high beam with the movement of the headlamp dimmer switch lever. With the headlamp dimmer switch in the high beam position the BCM sends a message via serial data to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator. Ground for the left headlamp assembly is provided at G101. Ground for the right headlamp assembly is provided at G102.

### 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 off switch parameter while turning the headlamp switch ON and OFF. The parameter should change between Inactive and Active.

⇒ | If the parameter does not change between the commanded states, refer to Headlamp 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 Inactive and Active.

⇒ | If the parameter does not change between the commanded states, refer to Headlamp 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 Inactive and Active.

⇒ | If the parameter does not change between the commanded states, refer to Headlamp Switch Malfunction.

4. Observe the scan tool headlamp on switch parameter while turning the headlamp switch ON and OFF. The parameter should change between Inactive and Active.

⇒ | If the parameter does not change between the commanded states, refer to Headlamp Switch Malfunction.

### 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 Off 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 BCM.

5. 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.

6. 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.

7. Verify the scan tool Headlamp On 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 BCM.

8. 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.

9. 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.

10. 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.

11. 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.

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

#### Headlamps Malfunction - Low Beam

1. Ignition OFF, disconnect the low beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 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 30 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the low beam relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 85 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 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 the harness connector at the inoperative low beam headlamp.
8. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the low beam headlamps illuminate.

⇒ | If the low beam headlamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative low beam headlamp.

9. Connect a test lamp between the B+ circuit terminal 85 and the control circuit terminal 86.
10. Command the Low Beam Headlamps 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.

11. If all circuits test normal, test or replace the low beam relay.

#### Headlamps Malfunction - High Beam

1. Ignition OFF, disconnect the high beam relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 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 30 and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the high beam relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 85 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 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 the harness connector at the inoperative high beam headlamp.
8. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the high beam headlamps illuminate.

⇒ | If the high beam headlamps do not illuminate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the inoperative high beam headlamp.

9. Connect a test lamp between the B+ circuit terminal 85 and control circuit terminal 86.
10. Command the High Beam Headlamps 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.

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

#### 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 Bulb Replacement

• | Relay Replacement

• | Turn Signal Multifunction Switch Replacement

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