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 B257A 00: Headlamp Switch Input Signal Mismatch

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Flash to Pass Switch Signal | 1 | 1 | 1 | --
Headlamp Switch High Beam Signal | 1 | 1 | 1 | --
Headlamp Switch Headlamps ON Signal | B257A 00 | 1 | 1 | --
Headlamp Switch Headlamps OFF Signal | B257A 00 | 1 | 1 | --
Park Lamp Switch ON Signal | 2 | B257A 00 | 2 | --
Headlamp High Beam Relay Control | 1 | 1 | B2580 00 | --
Headlamp Low Beam Relay Control | 1 | 1 | B2575 00 | --
LF High Beam Headlamp Control | 1 | 1 | 1 | --
LF Low Beam Headlamp Control | 1 | 1 | 1 | --
RF High Beam Headlamp Control | 1 | 1 | 1 | --
RF Low Beam Headlamp Control | 1 | 1 | 1 | --
LF Headlamp Ground | -- | 1 | -- | --
RF Headlamp Ground | -- | 1 | -- | --
Headlamp and Panel Dimmer Switch Ground | -- | 1 | -- | --
Turn Signal/Multifunction Switch Ground | -- | 1 | -- | --
1. Headlamps Malfunction 2. Park, License, and/or Tail Lamps Malfunction

### Circuit/System Description

The body control module (BCM) supplies a B+ reference voltage through each of the headlamp switch signal circuits to the headlamp switch. When the headlamp switch is in the AUTO position, all headlamp switch signal circuits to the BCM are open and the BCM operates in the automatic mode. When the headlamp switch is turned to the PARK position, only the park lamp switch signal circuit is pulled low signaling the BCM park lamps ON request. When the headlamp switch is turned to the HEAD position, the park lamp and headlamp switch signal circuits are both pulled low, signaling the BCM the headlamps ON request. When the headlamp switch is turned to the OFF position, only the headlamp OFF switch signal circuit is pulled low, signaling the BCM the lights off request.

### Conditions for Running the DTC

• | Battery voltage must be between 9-16 volts.

• | Headlamp and panel dimmer switch cycled between the AUTO, PARK, HEAD, and OFF positions.

### Conditions for Setting the DTC

The BCM receives a mismatch signal between the headlamps OFF signal circuit, the headlamps ON signal circuit, and the park lamps ON signal circuit.

### Action Taken When the DTC Sets

The BCM disregards the headlamp switch input and defaults to automatic headlamp function.

### 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/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

1. Ignition OFF, disconnect the harness connector at the headlamp and panel dimmer switch.
2. Ignition ON, verify the scan tool Headlamp Switch parameter is Off.

⇒ | If not the specified value, test the signal circuit terminal 1 for short to ground. If the circuit tests normal, replace the BCM.

3. Verify the scan tool Auto Headlamp Disable Switch parameter is Inactive.

⇒ | If not the specified value, test the signal circuit terminal 3 for short to ground. If the circuit tests normal, replace the BCM.

4. Verify the scan tool Park Lamp Switch parameter is Off.

⇒ | If not the specified value, test the signal circuit terminal 5 for short to ground. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 1 and ground. Verify the scan tool Headlamp Switch parameter is On.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuits test normal replace the BCM.

6. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto Headlamp Disable Switch parameter is Active.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Install a 3A fused jumper wire between the signal circuit terminal 5 and ground. Verify the scan tool Park Lamp Switch parameter is On.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

8. If all circuits test normal, test or replace the headlamp and panel dimmer switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement

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