"The Fiesta ST does not have an actual AAT (ambient) sensor that reports directly to the ECU, so it relies on the ECU to infer temperature via algorithms in place that watch ECT, IAT, CAT, and VSS. There are settings in the ECU to infer this temperature at faster rates with less requirements, but typically it is still grossly inaccurate for anything in need of compensation.
To top this, the Fiesta ST instrument panel is not connected to the ECU along the same CANbus stream like the Focus ST. This means the inferred temperature is not shared with the IPC, and it derives a value on its own." - Braden Berger, Cobb Reverse Engineer