Service Information

Volt

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
Indicator/Multifunction Switch Sidelights ON Signal	2	B257A 00	2	--
Indicator/Multifunction Switch Headlamps OFF Signal	B257A 00	1	1	--
Indicator/Multifunction Switch Headlamps ON Signal	B257A 00	1	1	--
Indicator/Multifunction Switch Ground	--	1	--	--
1. Headlamps Malfunction 2. Sidelight, Number Plate, and/or Tail Lamps Malfunction

For headlamp operation, the body control module (BCM) monitors three signal circuits from the indicator/multifunction switch. When the indicator/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 (DRL) ON and OFF. When the indicator/multifunction switch is placed in the OFF position, the indicator/multifunction switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the indicator/multifunction switch in the sidelights position, the indicator/multifunction switch sidelights ON signal circuit is grounded, indicating that the sidelights have been requested. When the indicator/multifunction switch is in the headlamp position, both the indicator/multifunction switch sidelights ON signal circuit and the indicator/multifunction switch headlamps ON signal circuit are grounded. The BCM responds by commanding the sidelights and headlamps ON.

Conditions for Running the DTC

Battery voltage must be between 9-16V.

Conditions for Setting the DTC

•	The BCM detects an open/high resistance in the indicator/multifunction switch sidelights ON signal circuit.

•	The BCM detects a short to ground in the indicator/multifunction switch headlamps ON signal circuit.

•	The BCM detects a short to ground in the indicator/multifunction switch headlamps OFF signal circuit.

Action Taken When the DTC Sets

•	When DTC B257A 00 is present on the indicator/multifunction switch headlamps OFF signal circuit, the dipped beam headlamps are always ON in the AUTO position. The indicator/multifunction switch operates in all positions other than AUTO. The AUTO headlamp defeat is inoperative.

•	When DTC B257A 00 is present on the indicator/multifunction switch headlamps ON signal circuit, the dipped beam headlamps are always ON. The BCM disregards all indicator/multifunction switch inputs.

•	When DTC B257A 00 is present on the indicator/multifunction switch sidelights ON signal circuit, the sidelights and dipped beam headlamps are inoperative in the SIDELIGHTS and headlamps positions. Headlamps and sidelights 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

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 Testing

Vehicle OFF, disconnect the harness connector at the S78 Indicator/Multifunction Switch.
Vehicle OFF, all doors closed, all accessories OFF, and wait 2 minutes. Test for less than 10 Ω between the ground circuit terminal 6 and ground.

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

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 Body Control Module.

Verify the scan tool Sidelights 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 Body Control Module.

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 Body Control Module.

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 Body Control Module.

Install a 3 A fused jumper wire between the signal circuit terminal 7 and ground. Verify the scan tool Sidelights 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 Body Control Module.

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 Body Control Module.

If all circuits test normal, replace the S78 Indicator/Multifunction Switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•	Indicator Multifunction Switch Replacement

•	Control Module References for BCM replacement, programming and setup