I find I have the Owner's Manual, and it states the ATS is standard. The manual is very generic, but might still help you. If you didn't get it with the coach, send me a Private Message with your EMailID and I'll send it to you.
Depending on the Spec Code of you ONAN GenSet, it probably does NOT have an Oil Level Sensor, so that can't cut it off. If it's a MicroQuiet 4KY, it's splash lubricated, so it can't have an Oil Pressure Sensor either. It's you job to be sure the oil stays full and that's it. No Oil Filter either.
It's very likely you'll need a new GenSet carburetor. Keep the discussion going and we'll see if we can help.