Buick Regal: 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
1. Headlamps Malfunction
2. Park, License, and/or Tail Lamps Malfunction
Circuit/System Description
For headlamp operation, the body control module (BCM) monitors three signal
circuits from the
headlamp switch. When the headlamp switch is in the AUTO position, the three
signal circuits are
unaffected and the BCM relies on the ambient light sensor input to turn the
headlamps and daytime
running lamps ON and OFF. When the headlamp switch is placed in the OFF
position, the headlamp
switch headlamps OFF signal circuit is grounded, indicating to the BCM that the
exterior lamps should
be turned OFF. With the headlamp switch in the PARK LAMPS position, the headlamp
switch park
lamps ON signal circuit is grounded, indicating that the park lamps have been
requested. When the
headlamp switch is in the HEADLAMP position, both the headlamp switch park lamps
ON signal circuit
and the headlamp 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 headlamp switch park
lamps ON signal circuit.
- The BCM detects a short to ground in the headlamp switch headlamps ON
signal circuit.
- The BCM detects a short to ground in the headlamp switch headlamps OFF
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.
- When DTC B257A 00 is present on the headlamp 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 ignition
cycles have occurred.
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Wiring Schematics
Connector End View Reference
COMPONENT CONNECTOR END VIEWS - INDEX
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 Testing
1. Ignition OFF, all doors closed, all accessories OFF, disconnect the
harness connector at the S30
Headlamp Switch. It may take up to 2 min for all vehicle systems to power down.
2. Test for less than 15 Ω between the ground circuit terminal 8 and ground.
- Ignition OFF.
- Test for less than 2 Ω in the ground circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, repair the open/high resistance in the ground
connection.
- Go to next step: If less than 15 Ω
3. Ignition ON.
4. Verify the scan tool Automatic Headlamps Disable Switch parameter is
Inactive.
- Ignition OFF, disconnect the X1 harness connector at the K9 Body Control
Module.
- Test for infinite resistance between the signal circuit terminal 3 and
ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance, replace the K9 Body Control Module.
- Go to next step: If Inactive
5. Install a 3 A fused jumper wire between the signal circuit terminal 3 and
ground.
6. Verify the scan tool Automatic Headlamps Disable Switch parameter is Active.
- Ignition OFF, disconnect the X1 harness connector at the K9 Body Control
Module, ignition
ON.
- Test for less than 1 V between the signal circuit terminal 3 and ground.
- If 1 V or greater, repair the short to voltage on the circuit.
- Go to next step: If less than 1 V
- Test for less than 2 Ω in the signal circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K9 Body Control Module.
- Go to next step: If Active
7. Verify the scan tool Park Lamps Switch parameter is Inactive.
- Ignition OFF, disconnect the X1 harness connector at the K9 Body Control
Module.
- Test for infinite resistance between the signal circuit terminal 5 and
ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance, replace the K9 Body Control Module.
- Go to next step: If Inactive
8. Install a 3 A fused jumper wire between the signal circuit terminal 5 and
ground.
9. Verify the scan tool Park Lamps Switch parameter is Active.
- Ignition OFF, disconnect the X1 harness connector at the K9 Body Control
Module, ignition
ON.
- Test for less than 1 V between the signal circuit terminal 5 and ground.
- If 1 V or greater, repair the short to voltage on the circuit.
- Go to next step: If less than 1 V
- Test for less than 2 Ω in the signal circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K9 Body Control Module.
- Go to next step: If Active
10. Verify the scan tool Headlamps On Switch parameter is Inactive.
- Ignition OFF, disconnect the X1 harness connector at the K9 Body Control
Module.
- Test for infinite resistance between the signal circuit terminal 1 and
ground.
- If less than infinite resistance, repair the short to ground on the
circuit.
- If infinite resistance, replace the K9 Body Control Module.
- Go to next step: If Inactive
11. Install a 3 A fused jumper wire between the signal circuit terminal 1 and
ground.
12. Verify the scan tool Headlamps On Switch parameter is Active.
- Ignition OFF, disconnect the X1 harness connector at the K9 Body Control
Module, ignition
ON.
- Test for less than 1 V between the signal circuit terminal 1 and ground.
- If 1 V or greater, repair the short to voltage on the circuit.
- Go to next step: If less than 1 V
- Test for less than 2 Ω in the signal circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K9 Body Control Module.
Go to next step: If Active
13. Test or replace the S30 Headlamp Switch.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
- Headlamp Switch Replacement
- Control Module References for BCM replacement, programming, and setup
READ NEXT:
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.
Diag
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.
Diag
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.
Diag
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