B257A

DTC B257A

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of the diagnostic category.

DTC Descriptor
DTC B257A 00
- Headlamp Switch Input Signals Mismatch

Diagnostic Fault Information





Circuit/System Description

When the headlamp 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 headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit are both open and have no ground signal. When the headlamp 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 V.

Conditions for Setting the DTC

The BCM detects a short to ground on the headlamp switch headlamps OFF signal circuit or the headlamp switch headlamps ON signal circuit.

Actions 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 Schematics (Headlights Schematics)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the S30 headlamp switch.
2. Ignition OFF, test for less than 5 ohm between the ground circuit terminal 6 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Park Lamps Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the K9 BCM.

4. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the ground circuit terminal 6. Verify the scan tool Park Lamps Switch 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 K9 BCM.

5. Verify the scan tool Headlamps On Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 4 for a short to ground. If the circuit tests normal, replace the K9 BCM.

6. Install a 3 A fused jumper wire between the signal circuit terminal 4 and the ground circuit terminal 6. Verify the scan tool Headlamps On Switch 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 K9 BCM.

7. Verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive.

• If not the specified value, test the signal circuit terminal 5 for a short to ground. If the circuit tests normal, replace the K9 BCM.

8. Install a 3 A fused jumper wire between the signal circuit terminal 5 and the ground circuit terminal 6. Verify the scan tool Automatic Headlamps Disable Switch 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 K9 BCM.

9. If all circuits test normal, test or replace the S30 headlamp switch.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Headlamp, Instrument Panel Lamp Dimmer, and Fog Lamp Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming