Possible Causes

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

Possible causes are:

Open or shorted LFC/MFC/HFC circuit.
Open VPWR or IGN START/RUN circuit to low/medium/high speed FC relay.
Damaged low/medium/high FC relay.
Damaged PCM.