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 |
|---|---|---|---|---|
HDLP LO/HID Relay B+ | 1 | 1 | 1 | -- |
HI Beam Relay B+ | 1 | 1 | 1 | -- |
Flash to Pass Switch Signal | 1 | 1 | 1 | -- |
Headlamp Switch Headlamps ON Signal | B257A 00 | 1 | 1 | -- |
Headlamp Switch Headlamps OFF Signal | B257A 00 | 1 | 1 | -- |
Headlamp Switch High Beam Signal | 1 | 1 | 1 | -- |
Headlamp High Beam Relay Control | 1 | 1 | B2580 00 | -- |
Headlamp Low Beam Relay Control | 1 | 1 | B2575 00 | -- |
Headlamp and Panel Dimmer Switch Ground | -- | 1 | -- | -- |
LF Headlamp Ground | -- | 1 | -- | -- |
RF Headlamp 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
DTC B257A 00 will set when the BCM detects a short to ground on the headlamp switch headlamps OFF signal circuit or the headlamp switch headlamps ON 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. |
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 X2 harness connector at the BCM.
- Connect a test lamp between B+ and the signal circuit terminal 17.
- Turn the headlamp switch between the headlamp AUTO and headlamp OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
- Connect a test lamp between B+ and the signal circuit terminal 12.
- Turn the headlamp switch to the ON and OFF positions. The test lamp should turn ON and OFF as the switch is cycled.
- If all circuits test normal, replace the BCM.
| ⇒ | If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the headlamp switch. |
| ⇒ | If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch. |
| ⇒ | If the test lamp is always OFF, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the headlamp switch. |
| ⇒ | If the test lamp is always ON, test the signal circuit for a short to ground. If the circuit tests normal, replace the headlamp switch. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
