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 Descriptor

DTC B2575: Headlamp Control Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HDLP Relay B+ | 2 | 2 | -- | --
Headlamp Flash to Pass Signal | 4 | 4 | 4 | --
Headlamp High Beam Signal | 3 | 3 | 3 | --
Headlamp Switch ON Signal | 1 | 1 | 1 | --
Headlamp Switch OFF SIgnal | 1 | 1 | 1 | --
BEAM SEL Relay Control | B2582 00 | B2582 00 | B2583 00 | --
Headlamp Relay Control | 2 | 2 | B2575 00 | --
Headlamp Control | 2 | 2 | 2 | --
Headlamp and Panel Dimmer Switch Ground | -- | 1 | -- | --

1. Headlamp Switch Malfunction
2. Headlamp Malfunction -- Low Beam
3. Headlamp Malfunction -- High Beam
4. Turn Signal/Multifunction Switch Malfunction

### Circuit/System Description

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal, it will either turn ON the daytime running lamps (DRL) or the headlamps for auto headlamp operation. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the AUTO position, the headlights will either be turned ON or OFF, after an approximate 8 second delay depending on whether daylight or low light conditions are sensed. When the ambient light sensor signals the BCM for DRL operation in daylight conditions, the BCM illuminates the low beam headlamps at a reduced intensity utilizing the DRL relay. The DRL will operate when the ignition switch is in the RUN position, the headlamp and panel dimmer switch is in the AUTO position, the gear selector is not in the PARK position, and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.

### Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

The headlamp relay control circuit is shorted to voltage.

### Action Taken When the DTC Sets

The headlamps will be inoperative from the headlamp switch.

### Conditions for Clearing the DTC

• | This DTC will clear on current status after the condition for setting the fault is corrected and the ignition is cycled.

• | A history DTC will clear after 100 consecutive ignition cycles without a fault present.

### 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 Testing

#### Headlamp Relay Control Circuit Test

1. Ignition OFF, disconnect the HDLP relay.
2. Connect a test lamp between the relay control circuit terminal 86 and B+.
3. Ignition ON, command the headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF.

⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒ | If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

4. If all circuits test normal, test or replace the relay.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

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