My book tells me that fault code specifically says drain time is taking to long , this is an indication of either a clogged drain hose (or vent) or in some cases can be a worn down pump impeller (on heavy use machines) or in extreme cases your idea could be correct and the water level sensor is not showing a m/t basket so it gives this fault , a sure divider to this way of thinking is to watch machine (no soap or clothes) for moment it gets that fault , if theres water in drum then sensor is right and u need to took better at pump and drain hoses , if its M/T then sensor is wrong