DTC P1621: Code Word Does Not Match After Engine Cranking: 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 code word stored in Powertrain Control Module (PCM) and immobilizer unit does not match. Possible cause is:

Immobilizer system reprogram procedure was not performed correctly after replacing immobilizer unit or PCM.