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 Signal MismatchDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Flash to Pass Switch Signal | 1 | 1 | 1 | -- |
Headlamp Switch High Beam Signal | 1 | 1 | 1 | -- |
Headlamp Switch Headlamps ON Signal | B257A 00 | 1 | B257A 00 | -- |
Headlamp Switch Headlamps OFF Signal | B257A 00 | 1 | B257A 00 | -- |
Park Lamp Switch Park Lamps ON Signal | B257A 00 | B257A 00 | B257A 00 | -- |
Headlamp High Beam Relay Control | 1 | 1 | B2580 00 | -- |
Headlamp Low Beam Relay Control | 1 | 1 | B2575 00 | -- |
LF High Beam Headlamp Control | 1 | 1 | 1 | -- |
LF Low Beam Headlamp Control | 1 | 1 | 1 | -- |
RF High Beam Headlamp Control | 1 | 1 | 1 | -- |
RF Low Beam Headlamp Control | 1 | 1 | 1 | -- |
LF Headlamp Ground | -- | 1 | -- | -- |
RF Headlamp Ground | -- | 1 | -- | -- |
Headlamp Switch Ground | -- | 1 | -- | -- |
Turn Signal/Multifunction Switch Ground | -- | 1 | -- | -- |
1. Headlamps Malfunction | ||||
Circuit/System Description
When the headlamp switch is placed in the AUTO position, the body control module (BCM) receives a ground signal through the headlamp switch headlamps OFF signal circuit. The headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit are both open and have no ground signal. When the headlamp switch is placed in the PARK or HEAD position, the BCM will receive a ground signal through the headlamp switch headlamps ON signal circuit and the park lamp switch signal circuit. The headlamp switch headlamps OFF signal circuit will be open and have no ground signal
Conditions for Running the DTC
Battery voltage must be between 9-16 volts.
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
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
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, test or replace the headlamp switch.
| • | Headlamps ON signal terminal 1 |
| • | Park lamp ON signal terminal 2 |
| • | Headlamp 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 |
