Normal Operation - MKZ

WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

The Smart Junction Box (SJB) sends voltage signals to the passenger door lock control switch through the lock and unlock input circuits. When the lock or unlock switch is pressed, the corresponding voltage signal is routed to ground, signalling the SJB to lock or unlock the passenger doors and send a lock or unlock command to the Driver Door Module (DDM) over the Medium Speed Controller Area Network (MS-CAN).

The DDM sends voltage signals to the driver door lock control switch through the lock and unlock input circuits. When the lock or unlock switch is pressed, the corresponding voltage signal is routed to ground, signalling the DDM to lock or unlock the driver door and send a lock or unlock command to the SJB over the MS-CAN.

The door lock control switches have a dedicated ground circuit.

Fusion/Milan

The SJB sends voltage signals to both door lock control switches through the lock and unlock input circuits. When the lock or unlock switch is pressed, the corresponding voltage signal is routed to ground, signalling the SJB to lock or unlock the doors. The door lock control switches have a dedicated ground circuit.

DTC B2574 (Drivers Door LOCK Switch Short to Ground) - a continuous and on-demand DTC that sets when the DDM detects a short to ground on the lock input circuit. This code will also set if the driver door lock control switch is pressed for longer than 2 minutes.
DTC B2575 (Drivers Door UNLOCK Switch Short to Ground) - a continuous and on-demand DTC that sets when the DDM detects a short to ground on the unlock circuit. This code will also set if the driver door lock control switch is pressed for longer than 2 minutes.
DTC B2A25 (Trim Panel Lock Switch Circuit Failure) - an on-demand DTC that sets when the SJB detects a short to ground from the lock or unlock request input circuits. This DTC may also set if either of the door lock control switches are pressed for longer than 2 minutes.

This pinpoint test is intended to diagnose the following:

Wiring, terminals or connectors
Door lock control switch
DDM
SJB