Normal Operation
WARNING: This page is about a different car, the 2005 Mercury Mountaineer and 2005 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
The vehicle security module communicates with the diagnostic tool through the UART-based protocol (UBP) communications network circuit 693 (OG). If circuit 693 (OG) becomes open or shorted to ground, communications to that module will not be possible. Check circuit 693 (OG) between the vehicle security module C3203f and the DLC C251. The total resistance value must not be more than 5 ohms. If the resistance is more than 5 ohms there is an open in circuit 693 (OG), damage to the DLC C251, damage to the vehicle security module C3203f, or a problem in the in-line connectors.
The vehicle security module receives fused voltage through circuits 456 (DG/OG), 645 (WH/LB) and is grounded on circuit 1205 (BK).