2000 Pontiac Bonneville Service Engine Light, Low oil, gas gu

Cpl?'S I have, my service engine light is on and the car runs great, also my computer is telling me that my oil level is low which its not, its right right where the oil level should be, I also changed the supercharger oil and that is fine as well. I always check and make sure all my fluids are where they should be. My Last? Is MY gas gauge doesn't work, when I start the car it will go to full and then go right to empty or right after I start driving it. Any Idea's would be very helpful! Thanks