I replaced the pump on a previous PC, and I can do some stuff, but am not a mechanic, for sure. I got the replacement from Carol at the factory, and at a price less than from Thetford. I do like the macerator, and use it all the time....to each his own.
For sensors, it is most important to flush with fresh water after dumping, wait until the tank is 3/4 full before you dump, and use either the commercial holding tank stuff or a soap mixture (I've not used the mix but a friend of mine swears by it). Also, there is a sensor cleaner which might help the error.
Jack