DTC P1602: Immobilizer Unit To Pcm Communication Error: Notes
WARNING: This page is about a different car, the 2003 Mazda MPV and 2002 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
DO NOT crank engine before replacement PCM is programed to immobilizer system or PCM will be severely damaged. If test procedures require replacement of PCM on a vehicle equipped with immobilizer system, vehicle must be sent to authorized Mazda dealer to have replacement PCM programed.