2010 Cadillac CTS Sedan AWD V6-3.6L Page 200
Instructions) provides an overview of the diagnostic category.
DTC Descriptor
DTC B257A 00
- Headlamp Switch Input Signals Mismatch
Diagnostic Fault Information
Circuit/System Description
When the turn signal/multifunction 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 turn signal/multifunction switch headlamps ON signal circuit and the park lamp switch signal
circuit are both open and have no ground signal. When the turn signal/multifunction 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 V.
Conditions for Setting the DTC
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 (See: Diagrams/Electrical Diagrams/Lighting and Horns/System
Diagram/Headlights/Daytime Running Lights (DRL) Schematics)
* Exterior Lights Schematics (See: Diagrams/Electrical Diagrams/Lighting and Horns/System Diagram/Exterior Lights Schematics)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Description and Operation
Exterior Lighting Systems Description and Operation (See: Lighting and Horns/Description and Operation/Exterior Lighting Systems Description
