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.

### DTC Descriptors

DTC B2645 02: Ambient Light Sensor Circuit Short to Ground
DTC B2645 05: Ambient Light Sensor Circuit Short to Battery or Open

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Light Sensor Signal | B2645 02 | B2645 05 | B2645 05 | --
Headlamp - Low Beam Control - Right | 2 | 2 | 2 | --
Headlamp - Low Beam Control - Left | 2 | 2 | 2 | --
Ambient Light Sensor Low Reference | -- | 1 | 1 | --
Headlamp - Low Beam Ground - Right | -- | 2 | -- | --
Headlamp - Low Beam ground - Left | -- | 2 | -- | --
1. Daytime Running Lamps Malfunction 2. Headlamps 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 2-4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a low reference ground and a 5-volt reference signal to the ambient light sensor. The BCM monitors the daytime running lamps (DRL) ambient light sensor signal circuit to determine if outside lighting conditions are correct for either DRL or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In high outside light conditions the BCM will command the DRLs ON. In low light conditions, when the headlamps switch is in AUTO position, the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel the DRL operation.

### Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### B2645 02

This DTC will set when the BCM detects a short to ground in the DRL ambient light sensor signal circuit.

#### B2645 05

This DTC will set when the BCM detects a short to voltage or an open in the DRL ambient light sensor signal circuit.

### Action Taken When the DTC Sets

When DTC B2645 02 or B2645 05 is present, the ALC will default to ON.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

### 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 Testing

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, scan tool OFF, doors CLOSED, test for less than 20 ohms between the low reference circuit terminal B and ground.

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

3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is between 1-5 volts.

⇒ | If less than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the BCM.

⇒ | If greater than the specified range, test the signal circuit terminal A for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ambient Light Sensor Replacement

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