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 Sensor Signal | B2645 03 | B2645 07 | B2645 07 | --
DRL Relay Control | 1 | 1 | B2600 00 | --
Ambient Light Sensor Ground | -- | B2645 07 | -- | --
1. Daytime Running Lamps 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 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. 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 (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 by applying ground to the DRL relay via the DRL relay control circuit. When the BCM applies ground to the DRL relay control circuit, the DRL relay coil energizes causing the relay switch contacts to close. With the DRL relay switch contacts closed, battery voltage flows through the DRL 1 and DRL 2 fuses to the left and right LO BEAM fuses to the low beam headlamps. Any function or condition that turns on the headlamps will cancel DRL operation.

### 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 a short to ground in the ambient light sensor signal circuit.

#### B2645 07

The DTC will set when 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

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 5.0 ohms between the ground circuit terminal B and ground.

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

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 A for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the ground circuit terminal B. 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. If the circuit tests normal, replace the BCM.

5. 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