The fault signal can be clogged aeration lines pulling the motor down, electric motor failing, poor connections and more. The pumps may run fine, though the fault shows from voltage errors. A pump not working at all will fault. Removing the stern light will fault as no power flows. NO flow of power and the wrong levels show fault codes, and eventually shut that portion down. Too much or too little current basically. Some pumps will fault without water pulling the motor down for example, from too little amp draw.