Ford anti theft system comes on when driving?

Ford. Passive anti theft system comes on when driving for a second and shuts car off then car comes back on. The pats light flash's while this happens. Car has a chip ignition key any ideas?

Bad ignition switch, bad key fob or car's computer needs to be reprogrammed. Try using spare key fob. No joy, take car to a dealer or repair shop.

Got new key and it was reprogrammed. Didn't work. Was thinking transceiver. Dealer is the only one that can fix the transceiver.