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

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ambient Light Senor Signal | B2645 03 | B2645 07 | B2645 07 | --
Headlamp- Left Low Beam Control | 1 | 1 | 1 | --
Headlamp- Right Low Beam Control | 1 | 1 | 1 | --
Ambient Light Sensor Low Reference | -- | B2645 07 | B2645 07 | --
Headlamp- Right Low Beam Ground | -- | 1 | -- | --
Headlamp- Right Low Beam Ground | -- | 1 | -- | --
1. Headlamps Malfunction

### Circuit/System Description

The ambient light/sun load sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 0.2 and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a 5-volt reference signal to the ambient light sensor and the HVAC control module provides a low reference ground. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the low beam headlamps OFF. During low light conditions 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 BCM detects a short to ground in the ambient light sensor signal circuit.

#### B2645 07

The BCM detects a short to voltage or an open/high resistance in the ambient light sensor signal circuit.

### Actions Taken When the DTC Sets

• | Automatic lamp control (ALC) is inoperative.

• | The BCM defaults to low light status and commands the low beam headlamps 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

Headlights 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 sunload sensor.
2. Ignition ON, verify that a test lamp illuminates between the low reference circuit terminal C and B+.

⇒ | If the test lamp does not illuminate, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 4.65 volts.

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

4. Install a 3 A fused jumper wire between the signal circuit terminal D and the low reference circuit terminal C. Verify the scan tool Ambient Light Sensor parameter is less than 0.196 volts.

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

5. If all circuits test normal, replace the sunload sensor assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Sunload and Twilight Sentinel Sensor Replacement

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