DTC P1604: Key Id Numbers Unregistered In Pcm: Condition

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when key ID is not registered in Powertrain Control Module (PCM). Possible cause is:

Immobilizer system reprogram procedure was not performed after replacing PCM.