We recently purchases a 2007 Buick Lucerne. After getting gas, the message for fixing the gas cap came on. My husband tightened the gas cap and then the check engine light came on and has stayed on for the last 2 weeks. We took the car back to the dealer and they said they found nothing wrong and yet the check engine light stays on. We got the service record from the previous owner and they had taken the car back to the dealer about 4 or 5 times just before they traded the car in. What is causing the check engine light to come on? We are taking the car back to the dealer this week. At what point do we determine that we have a lemon? We really do like the car, but not if we have to pay for repairs that appear to go back to before we owned it.