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 | 4 | 4 | 4 | --
Headlamp Switch High Beam Signal | 4 | 4 | 4 | --
Headlamp Switch Headlamps ON Signal | B257A 00 | 1 | 1 | --
Headlamp Switch Headlamps OFF Signal | B257A 00 | 1 | 1 | --
Park Lamp Switch ON Signal | 5 | B257A 00 | 5 | --
Headlamp High Beam Relay Control | 3 | 3 | B2580 00 | --
Headlamp Low Beam Relay Control | 2 | 2 | B2575 00 | --
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 | -- | --
RF Headlamp Ground | -- | 2 | -- | --
Headlamp and Panel Dimmer Switch Ground | -- | 1 | -- | --
Turn Signal/Multifunction Switch Ground | -- | 4 | -- | --
1. Headlamp Switch Malfunction 2. Headlamps Malfunction - Low Beam 3. Headlamps Malfunction - High Beam 4. Turn Signal/Multifunction Switch Malfunction 5. Park, License, and/or Tail Lamps Malfunction

### Circuit/System Description

With the headlamp switch in the ON position, the headlamp switch headlamp ON signal circuit is grounded through the headlamp and panel dimmer 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 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 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, command the Parking Light Test On and Off with a scan tool. The park lamps should turn On and Off when commanded.

⇒ | If the park lamps do not turn On and Off when commanded, refer to Park, License, and/or Tail Lamps Malfunction.

2. Observe the scan tool Headlamp Switch parameter while turning the headlamp switch ON and OFF. The parameter should change between On and Off.

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

3. 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.

4. Observe the scan tool High Beam 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.

5. Observe the scan tool Auto Headlamp Disable Switch 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 Headlamp Switch Malfunction.

6. Command the Front Low Beam Test 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.

7. Command the Front High Beam Test 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

#### Headlamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 4 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 Switch parameter is Off.

⇒ | If not the specified value, test the signal circuit terminal 1 for short to ground. If the circuit tests normal, replace the BCM.

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

⇒ | If not the specified value, test the signal circuit terminal 3 for short to ground. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Headlamp Switch parameter is On.

⇒ | 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.

6. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto 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 BCM.

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

#### Turn Signal/Multifunction Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the turn signal/multifunction switch.
2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 4 and ground.

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

3. Verify the scan tool Flash to Pass 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.

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

⇒ | If not the specified value, test the signal circuit terminal 3 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 2 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.

6. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool High Beam 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.

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

#### Headlamps Malfunction - Low Beam without 9C1

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.

4. Verify that a test lamp illuminates between the B+ circuit terminal 86 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 2 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the inoperative low beam headlamp.

9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
10. Command the Front Low Beam Test 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 without 9C1

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.

4. Verify that a test lamp illuminates between the B+ circuit terminal 86 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 3 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 a short to ground or an open/high resistance. If the circuit tests normal, replace the inoperative high beam headlamp.

9. Connect a test lamp between the B+ circuit terminal 86 and the control circuit terminal 85.
10. Command the Front High Beam Test 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 Tests 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 Switch Replacement

• | Headlamp Replacement

• | Underhood Electrical Center or Junction Block Replacement

• | Relay Replacement

• | Turn Signal Switch Replacement

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