For 1990-2009 cars

### Diagnostic Instructions

1. Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
2. Review Strategy Based Diagnosis for an overview of the diagnostic approach.
3. Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC B257A 00: Headlamp Switch Input Signals Correlation

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Headlamp Switch Input Signal | -- | B257B 03 | B257B 07 | B257A 00

### Circuit/System Description

When the headlamp switch is placed in the low beam or park position, the body control module (BCM) will receive a ground signal through the headlamp switch headlamps signal circuit and the park lamp switch signal circuit.

### Conditions for Running the DTC

The ignition is in ON, ACCESSORY or RUN position.

### Conditions for Setting the DTC

The BCM receives an unexpected signal along either the headlamp switch OFF circuit or the headlamp ON 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 BCM clears this code from current when the fault is removed from the system.

### 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 Verification

Ignition ON, turn the headlamp switch in the low beam position. The low beam lamps should be ON.

Turn the headlamp switch in the OFF position. The low beam lamps should be OFF.

### Circuit/System Testing

1. Ignition OFF, disconnect the S30 Headlamp Switch harness connector. Test for less than 5 Ω between the ground circuit terminal 6 and ground.

⇒ | If greater then the specified value, test the ground circuit for an open/high resistance.

2. Connect the S30 Headlamp Switch harness connector.
3. Disconnect the X1 harness connector at the K9 Body Control Module (BCM).
4. Connect a test lamp between B+ and the signal circuit terminal 16.
5. Turn the headlamp switch between the low beam and OFF position. The test lamp should turn ON and OFF as the switch is cycled.

⇒ | If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the S30 Headlamp Switch.

⇒ | If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the S30 Headlamp Switch.

6. If all circuits test normal, replace the K9 Body Control Module (BCM).

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the S30 Headlamp Switch harness connector. Turn the S30 Headlamp Switch in OFF position, test for less than 5 Ω between the terminal 6 and terminal 5.

⇒ | If greater than the specified value, replace the S30 Headlamp Switch.

2. Turn the S30 Headlamp Switch in PARK position, test for less than 5 Ω between the terminal 6 and terminal 3.

⇒ | If greater than the specified value, replace the S30 Headlamp Switch.

3. Turn the S30 Headlamp Switch in low beam position, test for less than 5 Ω between the terminal 6 and terminal 4.

⇒ | If greater than the specified value, replace the S30 Headlamp 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