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
--- | --- | --- | --- | ---
Headlamp Switch Signal | 3 | B3909 05 | B3909 05 | --
LF High Beam Headlamp Control | B2580 00 | B2580 05 | B2580 05 | --
RF High Beam Headlamp Control | B3866 00 | B3866 05 | B3866 05 | --
LF Low Beam Headlamp Control | B2575 00 | B2575 05 | B2575 05 | --
RF Low Beam Headlamp Control | B2699 00 | B2699 05 | B2699 05 | --
LF High Beam Headlamp Ground | -- | 2 | -- | --
RF High Beam Headlamp Ground | -- | 2 | -- | --
LF Low Beam Headlamp Ground | -- | 1 | -- | --
RF Low Beam Headlamp Ground | -- | 1 | -- | --
Headlamp Switch Ground | -- | 3 | -- | --
1. Headlamps Malfunction - Low Beam 2. Headlamps Malfunction - High Beam 3. Headlamp Switch Malfunction

### Circuit/System Description

The headlamp switch is supplied with voltage from the instrument panel cluster (IPC) by two signal circuits, the headlamps signal circuit and the park lamp signal circuit. When the headlamp switch is placed in either the AUTO or HEAD position, the headlamps signal circuit is provided with ground through the switch contacts of the headlamp switch to a common headlamp switch ground back to the IPC. The IPC interprets the flow of voltage and responds by sending a serial data message to the underhood electrical center (UEC) requesting the low beam headlamps be activated. The UEC responds by applying voltage to the left and right low beam headlamp control circuits illuminating the low beam headlamps. Ground for the left headlamp is supplied at G101 and the right headlamp receives ground 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

Ignition ON, observe the scan tool Low Beam Switch Status parameter while turning the headlamp switch ON and OFF. The parameter should change between Off and On.

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

⇒ | If the parameter changes between the commanded states, refer to Headlamps Malfunction.

### Circuit/System Testing

#### Headlamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Ignition OFF, verify a test lamp illuminates between B+ and the ground circuit terminal 11.

⇒ | If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the IPC.

3. Ignition ON, verify the scan tool Low Beam Switch Status parameter is Off.

⇒ | If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the IPC.

4. Install a 3A fused jumper wire between the signal circuit terminal 5 and ground. Verify the scan tool Low Beam Switch Status 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 IPC.

5. If all circuits test normal, replace the headlamp switch.

#### Headlamps Malfunction - Low Beam

1. Ignition OFF, disconnect the harness connector at the inoperative headlamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 10 and ground.

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

3. Connect a test lamp between the control circuit terminal 3 and ground.
4. 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 voltage. If the circuit tests normal, replace the UEC.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the UEC.

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

#### Headlamps Malfunction - High Beam

1. Ignition OFF, disconnect the harness connector at the inoperative headlamp.
2. Ignition OFF, exterior lamps OFF, test for less than 5 ohms between the ground circuit terminal 9 and ground.

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

3. Connect a test lamp between the control circuit terminal 2 and ground.
4. 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 voltage. If the circuit tests normal, replace the UEC.

⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the UEC.

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

#### High Beam Indicator Malfunction

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

⇒ | 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

• | High Intensity Discharge Headlamp Ballast Replacement

• | Headlamp Bulb Replacement - Left Side

• | Headlamp Bulb Replacement - Right Side

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