Possible Causes

WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 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 (DTCs P0603 or P1605).
Open KAPWR circuit (DTC P1633).
KAPWR to PCM interrupt/open (DTCs P0603 or P1605).
Damaged PCM (DTCs P0603, P1605, P1633 or P1639).
Reprogramming (DTCs P0603, P1605 or P1639).
Intermittent KAPWR circuit (DTCs P1633).