gas level, check engine, emission

Can anyone shed some light on these problems? When I start my 2001 passat the check engine light always comes on. Soon after, when I begin driving the emission light beeps briefly then disappears.

The only noticeable problem I've seen is that when I'm pumping gas in the car, for some reason the nozzels constantly clicks back and reads the tank as full, the gauge appears to work cause it does read decreases and increases in gas levels.

Help

the same thing happens, in my 01 passat. It seems to me that whenever the car is driven when it is low on gas and sometimes when I put regular (87 octane) gas an emissions light warning comes on and then goes off within the next couple of days. Definitly some kind of problem, haven't gone to the dealer to check it out.