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 MismatchDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Headlamp Switch Off | B257A 00 | 2, 3 | B257A 00 | -- |
Park Lamp Switch On | B257A 00 | B257A 00 | B257A 00 | -- |
Headlamp Switch On | B257A 00 | 1 | B257A 00 | -- |
Headlamp Ground | -- | 3, 4 | -- | -- |
| ||||
Circuit/System Description
The body control module (BCM) supplies a B+ reference voltage through each of the headlamp switch signal circuits to the headlamp switch. When the headlamp switch is in the AUTO position, all headlamp switch signal circuits to the BCM are open and the BCM operates in the automatic mode. When the headlamp switch is turned to the PARK position, only the park lamp switch signal circuit is pulled low signaling the BCM park lamps ON request. When the headlamp switch is turned to the HEAD position, the park lamp and headlamp switch signal circuits are both pulled low, signaling the BCM the headlamps ON request. When the headlamp switch is turned to the OFF position, only the headlamp off switch signal circuit is pulled low, signaling the BCM the lights off request.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The BCM receives a mismatched signal between the headlamps OFF signal circuit, the headlamp switch headlamps ON signal circuit, and the park lamp switch ON signal circuit.
Action Taken When the DTC Sets
The BCM disregards the headlamp switch input and defaults to automatic headlamp function.
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
Connector End View Reference
Lighting Systems Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
Ignition ON with the headlamp switch in the Auto position, observe the scan tool Exterior Lighting parameters listed below. All parameters should be Inactive.
| • | Auto Hdlp. Disable Sw. |
| • | Headlamp Switch |
| • | Park Lamp Switch |
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the headlamp switch.
- Ignition ON, test for B+ between the signal circuits listed below and ground.
- Install a 3A fused jumper wire between the signal circuit terminal 2 and ground. Verify the scan tool Parklamp Switch parameter is Active.
- If all circuits test normal, replace the headlamp switch.
| • | Headlamp switch headlamps ON signal terminal 1 |
| • | Park lamp switch ON signal terminal 2 |
| • | Headlamp switch OFF signal terminal 3 |
| ⇒ | If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
| ⇒ | 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 BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
