Possible Causes

WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes are:

Battery terminal corrosion or loose connections (P0603 or P1605).
Open KAPWR circuit (P1633).
KAPWR to PCM interrupt/open (P0603 or P1605).
Damaged PCM (P0603, P1605 or P1633).
Reprogramming (P0603 or P1605).
Intermittent KAPWR circuit (P1633).