The ceiling bathroom light has a motion detector which would turn on the light when someone entered the bathroom. The wall switch still works to turn on the light. Can the sensor be replaced or is it necessary to replace the whole unit?

It would all depend on the sensor.

Can you get to the sensor and see how it is wired and get an ID on it.

Fan model #?

Likely integrated into motor. Easiest is buy new motor and swap motor if integrated. Toss new housing and keep extra cover just in case or to swap if it yellows.

Check to see if different components have different part numbers. If so you can likely order, if not probably all one unit.

OK thanks Jesse.