Normal Operation
WARNING: This page is about a different car, the 2009 Mercury Milan, 2009 Lincoln MKZ, and 2009 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.
When the headlamp switch is in the AUTOLAMPS ON position, the smart junction box (SJB) monitors the light sensor by sending a voltage reference signal through circuit VLF14 (BU/BN). Ambient lighting to the light sensor changes the voltage by varying the resistance to ground. Ground for the light sensor is provided by circuit GD116 (BK/VT).
When the ambient level has reached a point (determined by the internal programming of the SJB), the SJB provides voltage to the exterior lamps.
- DTC B1793 (Autolamp Sensor Input Circuit Short To Ground) - is a continuous DTC that sets when the SJB detects a short to ground on the light sensor input circuit.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Light sensor
- SJB