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 03: Ambient Light Sensor Circuit Below Threshold
DTC B2645 07: Ambient Light Sensor Circuit Above Threshold

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Light Sensor Signal Circuit | B2645 07 | B2645 03 | B2645 07 | B2645 03 or B2645 07
Ambient Light Sensor Ground Circuit | -- | B2645 03 | -- | B2645 03 or B2645 07

### 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 depending on outside lighting conditions. The body control module (BCM) provides a 10-volt reference signal to the ambient light sensor. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight 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.

### Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

#### B2645 03

The DTC will set when the BCM detects voltage is low in the ambient light sensor signal circuit.

#### B2645 07

The DTC will set when the BCM detects voltage is above 10 volts in the ambient light sensor signal circuit

### Action Taken When the DTC Sets

When DTC B2645 03 or B2645 07 is present, the ALC will default to ON.

### Conditions for Clearing the DTC

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

• | A scan tool CLEAR DTCs command is issued.

• | 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

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Testing

1. Ignition OFF, disconnect the ambient light sensor.
2. Ignition ON, monitor the Ambient Light Sensor parameter in the BCM data list with a scan tool.

⇒ | If the scan tool parameter is less than 7 volts, locate and repair an open, high resistance, or short to ground in the ambient light sensor signal circuit, or replace the ambient light sensor.

⇒ | If the scan tool parameter is greater than 10.5 volts, locate and repair a short to voltage in the ambient light sensor signal circuit.

3. If circuits test OK, replace the BCM.

### 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