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DTC B257A

DTC B257A

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 Correlation Malfunction

Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Headlamp Switch Park Lamp Signal 2 B257A 00 2 -
Headlamp Switch On Signal B257A 00 1 1 -
Headlamp Switch Headlamps Off Signal B257A 00 1 1 -
Headlamp Switch Ground - 1 - -
1. Headlight Auto Function Only 2. Headlight Auto Function Disabled


Circuit/System Description

The body control module (BCM) monitors the 12 V signal circuits for the headlamps off signal, headlamps on signal and the park lamp on signal circuits. When the headlight control switch is selected to the desired headlamp function, the signal circuit is pulled to ground and the BCM will detect the voltage drop in that signal circuit and will command the appropriate lights to turn on or turn off.

Conditions for Running the DTC

The ignition is in the 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 automatic headlamps will malfunction.

Conditions for Clearing the DTC


• The DTC will be current for as long as the fault is present.

• When the fault is no longer present, the DTC will be a history DTC.

• A history DTC will clear after 50 ignition cycles.


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 Verification

Ignition ON, observe the scan tool Headlamps On Switch, Park Lamps Switch and Automatic Headlamps Disable Switch parameters while selecting the headlamp control switch between the Off, park lamps and headlamps settings. Each parameter should be Inactive and change to Active as each setting is selected.

Circuit/System Testing


1. Ignition OFF, disconnect the harness connector at the S30 headlamp switch.

2. Ignition OFF, test for less than 30 Ω between the ground circuit terminal 6 and ground.

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

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

5. 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.

6. 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 parameter is Active.

7. 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.

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

9. 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.

10. 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 parameter is Active.

11. 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.

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

13. 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.

14. 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 parameter is Active.

15. 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.

16. If all circuits test normal, test or 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, programming and setup