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 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 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/Daytime Running Lights (DRL) Schematics (Headlights/Daytime Running Lights (DRL) Schematics)
* Exterior Lights Schematics (Exterior Lights Schematics)

Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Exterior Lighting Systems Description and Operation (Exterior Lighting Systems Description and Operation)
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 BCM.
2. Connect a test lamp between B+ and the signal circuit terminal 23.
3. Cycle the headlamp switch between the AUTO and OFF positions. 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 turn signal/multifunction switch.
• If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.

4. Ignition OFF, disconnect the X2 harness connector at the BCM.
5. Connect a test lamp between B+ and the signal circuit terminal 12.
6. Cycle the headlamp switch between the HEAD and OFF positions. 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 turn signal/multifunction switch.
• If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.

7. Connect a test lamp between B+ and the signal circuit terminal 8.
8. Cycle the headlamp switch between the PARK and OFF positions. 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 turn signal/multifunction switch.
• If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit test normal, replace the turn signal/multifunction switch.

9. If all circuits test normal, replace the BCM.

Repair Instructions

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

* Turn Signal Multifunction Switch Replacement (Turn Signal Multifunction Switch Replacement)
* Control Module References (Programming and Relearning) for BCM replacement, setup, and programming