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 | 1 | 1 | -- | --
Ambient Light Sensor Low Reference Signal Circuits | -- | 1 | 1 | --
DRL Ambient Light Sensor | 1 | 1 | 1 | --
1. DRL Inoperative

### Conditions for Running the DTC

The low beam headlamps operate at reduced intensity when in daytime running lamps (DRL) mode. The DRL relay is soldered into the underhood fuse block circuit board. The ground circuit to the switch side or the DRL relay has a resistor in-line to reduce the intensity of the low beam headlamps for DRL operation. The body control module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient outside light level. Under daylight conditions the BCM grounds the DRL relay control circuit energizing the DRL control relay. The now closed relay supplies ground directly to the low beam headlamps now illuminate with reduced intensity. The DRL relay is ground at G203. Any time the headlamps are illuminated the DRL will not illuminate. Manual park lamps do not effect DRL operation.

### Diagnostic Aids

• | A short to ground or open/high resistance in the ambient light sensor circuit

• | The ambient light sensor with an open/high resistance within it

• | Inspect the daytime running lamps (DRL) resistor located on the left frame rail for cracks and corrosion. Refer to Daytime Running Lamps (DRL) Resistor Replacement . A failure of the resistor due to corrosion brought on by the original fastening procedure to the frame has been common on this vehicle.

• | If replacing the DRL resistor please pay attention to any replacement revisions.

### Reference Information

#### Schematic Reference

Interior Lights Schematics

#### Connector End View Reference

Lighting Systems Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Data Definitions

• | Scan Tool Data List

• | Scan Tool Output Controls

### Circuit/System Verification

Ignition ON, the headlamp switch in the AUTO position. Observes the headlamps, the headlamps should be ON.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the DRL ambient light sensor.
2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit and ground.

⇒ | If greater than 1 ohm, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit and ground.

⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, test or replace the DRL ambient light sensor.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the DRL ambient light sensor.
2. Sweep the sensor through the entire range while monitoring the resistance between the signal terminal and the low reference terminal. The resistance should vary between 13-23 M ohms without any spikes or dropouts.

⇒ | If the resistance is not within the specified range or is erratic, replace the DRL ambient light sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Daytime Running Lamps (DRL) Resistor Replacement

• | Ambient Light Sensor Replacement

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