For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - VehicleDiagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based DiagnosisStrategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure InstructionsDiagnostic 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 | B2645 03 | B2645 03 | B2645 07 | --
Ground | -- | 1 | -- | --
1. Daytime Running Light Malfunction

### Circuit/System Description

The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 1.4-4.5 V depending on outside lighting conditions. The body control module (BCM) monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights or automatic lamp control when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the daytime running lights ON. During low light conditions the BCM will command the low beam headlamps ON.

### 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, observe the scan tool Ambient Light Sensor parameter. The reading should be between 1.4-4.5 V and change with ambient light changes.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the B10B Ambient Light/Sunload Sensor.
2. Test for less than 5 Ω between the low reference circuit harness connector terminal 6 and ground.

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

3. Connect the harness connector at the B10B Ambient Light/Sunload Sensor.
4. Disconnect the X2 harness connector at the K9 Body Control Module (BCM).
5. Ignition ON, test for 4.8-5.2 V between the signal circuit X2 harness connector terminal 10 and ground.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the B10B Ambient Light/Sunload Sensor.

⇒ | If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the B10B Ambient Light/Sunload Sensor.

6. If all circuits test normal, replace the K9 Body Control Module (BCM).

### Component Testing

#### Static Test

1. Ignition ON, observe the scan tool Ambient Light Sensor parameter. The reading should be between 1.4-4.5 V and change with ambient light changes.
2. Test the B10B Ambient Light/Sunload Sensor by varying the ambient light while monitoring the sensors voltage output.
3. Verify that the voltage output is within the range of the specification.

⇒ | If not within the specified range, replace the B10B Ambient Light/Sunload Sensor.

### Repair Instructions

Perform the Diagnostic Repair VerificationDiagnostic Repair Verification after completing the diagnostic procedure.

• | Tail Lamp Replacement

• | Sun Load Temperature and Headlamp Automatic Control Ambient Light Sensor Replacement

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