Test No. 20: Key Reminder Buzzer Does Not Sound With Any Door Open (Key Removed From Ignition)
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.
Remove steering column cover. Remove key reminder switch. Check for continuity between switch terminals. Continuity should exist when key is inserted in lock. Continuity should not exist when key is removed. If key reminder switch is okay, replace CPU. If key reminder switch is bad, replace ignition lock.