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 each diagnostic category.
DTC Descriptor
DTC B257A 00
- Headlamp Switch Input Signals Correlation Malfunction
Diagnostic Fault Information
Circuit/System Description
For headlamp operation, the body control module (BCM) monitors three signal circuits from the turn signal/multifunction switch. When the turn signal/multifunction switch is in the AUTO position, the three signal circuits are open and the BCM relies on the ambient light sensor input to turn the headlamps and daytime running lamps (DRLs) ON and OFF. When the turn signal/multifunction switch is placed in the OFF position, the turn signal/multifunction switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the turn signal/multifunction switch in the PARK LAMPS position, the turn signal/multifunction switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the turn signal/multifunction switch is in the HEADLAMP position, both the turn signal/multifunction switch park lamps ON signal circuit and the turn signal/multifunction switch headlamps ON signal circuit are grounded. The BCM responds by commanding the park lamps and headlamps ON.
Conditions for Running the DTC
Battery voltage must be between 9-16 V.
Conditions for Setting the DTC
* The BCM detects an open/high resistance in the turn signal/multifunction switch park lamps ON signal circuit.
* The BCM detects a short to ground in the turn signal/multifunction switch headlamps ON signal circuit.
* The BCM detects a short to ground in the turn signal/multifunction switch headlamps OFF signal circuit.
Actions Taken When the DTC Sets
* When DTC B257A 00 is present on the turn signal/multifunction switch headlamps OFF signal circuit, the low beam headlamps are always ON in the AUTO position. The turn signal/multifunction switch operates in all positions other than AUTO. The AUTO headlamp defeat is inoperative.
* When DTC B257A 00 is present on the turn signal/multifunction switch headlamps ON signal circuit, the low beam headlamps are always ON. The BCM disregards all turn signal/multifunction switch inputs.
* When DTC B257A 00 is present on the turn signal/multifunction switch park lamps ON signal circuit, the park lamps and low beam headlamps are inoperative in the PARK and HEAD positions. Headlamps and park lamps operate in AUTO position.
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 vehicle ON/OFF switch cycles have occurred.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference
Component Connector End Views Hybrid/EV Battery Pack X1
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. Vehicle OFF, disconnect the harness connector at the S78 turn signal/multifunction switch.
2. Vehicle OFF, all doors closed, all accessories OFF, and wait 2 minutes. Test for less than 10 ohm between the ground circuit terminal 6 and ground.
• If greater then the specified range, test the ground circuit for an open/high resistance.
3. Vehicle in Service Mode, verify the scan tool Automatic Headlamps Disable Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the K9 BCM.
4. Verify the scan tool Park Lamps Switch parameter is Inactive.
• If not the specified value, test the signal circuit terminal 7 for a short to ground. 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 2 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 9 and ground. Verify the scan tool Automatic Headlamps Disable 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 K9 BCM.
7. Install a 3 A fused jumper wire between the signal circuit terminal 7 and ground. Verify the scan tool Park Lamps 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 K9 BCM.
8. Install a 3 A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Headlamps On 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 K9 BCM.
9. If all circuits test normal, replace the S78 turn signal/multifunction switch.
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