Be curious to hear what 'fuel sensor' is located inside the engine. I would recommend removing the tornado thing, and driving for a while and see if the idiot light goes off and if it does, wait a while and ask onstar to recheck for codes.
Onstar people are ok, but they are not engineers or technicians.
A filter replacement should do nothing, and I mean that literally.
From the factory, it should not have too much oil which is what causes the major problem with sensors.