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.

### 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 - with LHD | -- | B2645 07 | B2645 07 | --
Ambient Light Sensor Ground | -- | B2645 07 | 2 | --
Headlamp- Right Low Beam Ground | -- | 1 | -- | --
Headlamp- Right Low Beam Ground | -- | 1 | -- | --
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction

### Circuit/System Description

#### With Manual HVAC

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 which is permanently grounded at G201. 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. The DRLs consists on the low beam headlamps illuminated at full intensity. During low light conditions the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation.

#### LHD With Automatic HVAC

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 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. The DRLs consists on the low beam headlamps illuminated at full intensity. During low light conditions the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation.

#### RHD With Automatic HVAC

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 which is permanently grounded at G201. 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. The DRLs consists on the low beam headlamps illuminated at full intensity. During low light conditions the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation.

### Reference Information

#### Schematic Reference

Headlights/Daytime Running Lights (DRL) 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

1. Ignition ON, with a scan tool command the Front Low Beam Test ON and OFF. The low beam headlamps should turn ON and OFF when changing between the commanded states.

⇒ | If the low beam headlamps do not turn ON and OFF when commanded, refer to Headlamps Malfunction.

⇒ | If the low beam headlamps turn ON and OFF when commanded, refer to Ambient Light Sensor Malfunction.

2. Ignition ON, park brake released, verify with a scan tool the Park Brake Switch parameter displays Inactive.

⇒ | If not the specified value, refer to Symptoms - Hydraulic Brakes.

### Circuit/System Testing

#### Ambient Light Sensor Malfunction - with Manual HVAC

1. Ignition OFF, disconnect the harness connector at the ambient light sensor.
2. Ignition OFF, verify that a test lamp illuminates between the ground circuit terminal B and B+.

⇒ | If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance.

3. If all circuits test normal, replace the BCM.

#### Ambient Light Sensor Malfunction - LHD with Automatic HVAC

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. If all circuits test normal, replace the BCM.

#### Ambient Light Sensor Malfunction - RHD with Automatic HVAC

1. Ignition OFF, disconnect the harness connector at the sunload sensor.
2. Ignition ON, verify that a test lamp illuminates between the ground circuit terminal C and B+.

⇒ | If the test lamp does not illuminate, test the ground circuit for a short to voltage or an open/high resistance.

3. If all circuits test normal, replace the BCM.

### 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