Ford Focus Owners Manual: Principle of operation

Engine immobiliser

...

Coded keys

Note: Do not shield your keys with metal objects. This may prevent the receiver from recognising your key as a valid one. Note: Have all of your remaining keys erased and recoded if you lose a key ...

More about Ford Focus:

Ford Focus Anti-Lock Control
Anti-Lock Braking The ABS consists of the following components: ABS module — attached to the Hydraulic Control Unit (HCU) , but can be serviced separately from the HCU . Front wheel speed sensors — one sensor is located in each front wheel knuckle. The sensors are serviced separa ...