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
--- | --- | --- | --- | ---
Ambient Light Sensor Signal | B2647 00 | B2648 00 | B2648 00 | --
Ambient Light Sensor Low Reference | -- | 2 | 2 | --
Daytime Running Lamp Relay Control | B2602 00 | B2602 00 | B2603 00 | --
Daytime Running Lamp - Left Voltage Supply | 2 | 2 | 2 | --
Daytime Running Lamp - Right Voltage Supply | 2 | 2 | 2 | --
Headlamp - Left Front Low Beam Supply Voltage | 1 | 1 | 1 | --
Headlamp - Right Front Low Beam Supply Voltage | 1 | 1 | 1 | --
Daytime Running Lamp - Left Ground | -- | 2 | -- | --
Daytime Running Lamp - Right Ground | -- | 2 | -- | --
Headlamp - Left Front Ground | -- | 1 | -- | --
Headlamp - Right Front Ground | -- | 1 | -- | --

1. Headlamps Malfunction
2. Daytime Running Lamps Malfunction

### Circuit/System Description

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the daytime running lamps (DRL) or the headlamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. When the ambient light sensor signals the BCM for DRL operation in daylight conditions, the BCM illuminates the low beam headlamps at a reduced intensity utilizing the DRL relay. The DRL will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

### Diagnostic Aids

Verify that the headlamps operate normal in the manual mode prior to diagnosing a DRL condition.

### Reference Information

#### Schematic Reference

Exterior Lights 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, command the daytime running lamps ON and OFF with a scan tool. The daytime running lamps should turn ON and OFF.

### Circuit/System Testing

1. Ignition OFF, disconnect the DRL relay.
2. Ignition ON, verify that a test lamp does not illuminate between the daytime running lamp 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 DRL circuit fuse is open, test the control circuit terminal 87 for a short to ground. If the circuit tests normal, test or replace the DRL relay.

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. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the DRL headlamps are on.

⇒ | If the DRL headlamps are not on, test the control circuit for a short to ground or an open/high resistance.

6. Connect a test lamp between the B+ circuit terminal 86 and the relay control circuit terminal 85.
7. Command the daytime running lamps 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.

8. If all circuits test normal, test or replace the DRL relay.
9. Ignition OFF, disconnect the inoperative DRL.
10. Test for less than 5.0 ohms between the ground circuit terminal B and ground.

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

11. Connect a test lamp between the control circuit terminal A and ground. Command the DRL lamps ON and OFF with a scan tool. The test lamp should turn ON and OFF between the commanded states.

⇒ | If the test lamp is always ON, test the control circuit for a short to voltage.

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

12. If all circuits test normal, test or replace the inoperative DRL.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, programming, and setup.