This post details the PATS security system in the Australian delivered Duratec engined Ford Focus. It follows on from this post.
The PATS (Passive Anti Theft System) essentially forms the vehicles immobiliser. Without the PATS system working, your Focus just wont start.
The thing that makes the system a little odd in this vehicle is the critical function performed by the instrument cluster. Not only is the cluster required for PATS operation, it has to be coded to match both the ECU and key!
The diagram below shows the layout of the components in the Focus PATS system.
The Instrument Cluster communicates with the Key ECU which is located beside the ignition cylinder, it includes a loop type antenna for wireless communication with the circuitry embedded in the key head. Communication with the cluster is by a independent serial bus.
The Cluster interacts with the Engine ECU through the high speed CAN bus which is shared with most other ECU's. The messages sent between these components perform many functions apart from the PATS feature.
