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 |
|---|---|---|---|---|
Headlamp Switch Off Signal | B257A 00 | 3 | -- | -- |
Park Lamp Switch On Signal | 5 | 4 | -- | -- |
Headlamp Switch On Signal | B257A 00 | 2 | -- | -- |
Headlamp Ground | -- | 2, 3, 4 | 2 | -- |
1. Headlamps Always On 2. Headlamps Inoperative From Switch 3. Unable To Turn OFF Automatic Headlamps 4. Park Lamps Inoperative From Switch 5. Park Lamps Always On | ||||
Circuit/System Description
When the headlamp switch is in the OFF position, the body control module (BCM) receives a ground signal through the headlamp switch OFF circuit and an open signal on the park lamp ON circuit and headlamps ON circuit. When the headlamp switch is in the PARK or HEAD position, the BCM receives an open signal through the headlamp switch OFF circuit and a ground signal through the park lamp ON circuit or headlamp ON circuit.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The BCM receives an unexpected signal along either the headlamp switch OFF circuit or the headlamp ON 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 BCM clears this code from current when the fault is removed from the system.
Reference Information
Schematic Reference
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 Verification
Ignition ON, headlamp switch to PARK, just the park lamps should illuminate.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the headlamp switch.
- Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.
- Ignition ON, verify the scan tool Auto Hdlp. Disable Sw. parameter is Inactive.
- Verify the scan tool Headlamp Switch parameter is Inactive.
- Verify the scan tool Parklamp Switch parameter is Inactive.
- If all circuits test normal, test or replace the headlamp switch.
| ⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance. |
| ⇒ | If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | If not the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the BCM. |
| ⇒ | If not the specified value, test the signal circuit terminal 2 for a short to ground. 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 |
