Been battling the damn "Service Engine Soon" light for the last 2 months. It keeps reading the system for the fuel vac. The shop said it can be caused by something as simple as a loose gas cap. They shut the light off each time. We've tried 2 different gas caps, I make sure it's on tight after each fill up. They've had the tank out twice trying too find the problem. This is a small local shop we've been dealing with, so I don't think they have all the equipment the dealership has. I just hate the thought of having too spend $100.00 for the dealership too even look at it but I think I'm going too have too. Car runs fine, but that damn light on the dash drives me bugchit. Car is the 2000 Alero with the 3.4 V6. It only comes on after the 2nd fill up and usely right under 1/2 a tank. Any GM guru's have any idea ???