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 Signals 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 Headlamps ON Signal | B257A 00 | 1 | 1 | --
Headlamp Switch Headlamps OFF Signal | B257A 00 | 1 | 1 | --
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 | -- | --
Turn Signal/Multifunction Switch Ground | -- | 1 | -- | --
1. Headlamps Malfunction

### Circuit/System Description

When the turn signal/multifunction switch is placed in the AUTO position, the body control module (BCM) receives a ground signal through the headlamp switch headlamps OFF signal circuit. The turn signal/multifunction switch headlamps ON signal circuit and the park lamp switch signal circuit are both open and have no ground signal. When the turn signal/multifunction switch is placed in the PARK or HEAD position, the BCM will receive a ground signal through the headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit. The headlamp switch headlamps OFF signal circuit will be open and have no ground signal.

### Conditions for Running the DTC

Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

DTC B257A 00 will set when the BCM detects a short to ground on the headlamp switch headlamps OFF signal circuit or the headlamp switch headlamps ON signal circuit.

### Action Taken When the DTC Sets

• | When DTC B257A 00 is present on the headlamp switch headlamps OFF signal circuit, the low beam headlamps are always ON in the AUTO position. The headlamp switch operates in all positions other than AUTO. The AUTO headlamp defeat is inoperative.

• | When DTC B257A 00 is present on the headlamp switch headlamps ON signal circuit, the low beam headlamps are always ON. The BCM disregards all headlamp switch inputs.

### 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 X1 harness connector at the turn signal/multifunction switch.
2. Ignition ON, test for B+ between the signal circuit terminals listed below and ground.

• | Headlamp switch headlamps ON signal terminal 2

• | Park lamp switch ON signal terminal 3

• | Headlamp switch OFF signal terminal 4

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

3. Connect a 3A fused jumper wire between the headlamp OFF signal circuit terminal 4 and ground. Verify the scan tool Auto Hdlp. Disable Sw. 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.

4. Connect a 3A fused jumper wire between the park lamp ON signal circuit terminal 3 and ground. Verify the scan tool Parklamp 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.

5. Connect a 3A fused jumper wire between the headlamps ON signal circuit terminal 2 and ground. Verify the scan tool Headlamp 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.

6. If all circuits test normal, replace the turn signal/multifunction switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Turn Signal Multifunction Switch Replacement

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