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 parking lamps or the headlamps are on, the smart junction box (SJB) sends a reference voltage signal to the instrument panel dimmer switch on circuit VLN18 (BU/WH), which is grounded by the SJB through circuit CLN27 (WH/BN). The SJB uses the reference voltage to determine the intensity of the back lighting desired by the operator.

For hardwired dimmable illumination sources, the SJB sends a pulse-width modulated (PWM) voltage on circuit VLN04 (VT/GY) and CLN04 (BU/BN) (Fusion, Milan only) based on the input received from the instrument panel dimmer switch.

For network controlled illumination sources, the SJB sends a message via the medium speed controller area network (MS-CAN). If the module receiving the back lighting message either does not receive the message or receives invalid data for greater than 5 seconds, the module defaults to full nighttime intensity. Full nighttime intensity is equivalent to the illumination level when the parking lamps are on, and the instrument panel dimmer switch is in the highest setting.

DTC B1247 (Panel Dim Switch Circuit Open) - sets when the reference voltage to the instrument panel dimmer switch exceeds the maximum allowable value. This can be caused by an open or short to voltage on circuit VLN18 (BU/WH). This DTC only sets as a continuous DTC.

This pinpoint test is intended to diagnose the following:

Wiring, terminals or connectors
Instrument panel dimmer switch
SJB