Yes, andrew_j. There are great benefit$ for establishing a professional rapport with a good mechanic. In the mean time, getting the codes from McParts stores and posting to a forum such as this could save quite a bit of money. However, when the loose cap, or any malfunction, trips the CEL it will remain on for many days and miles even though the cap or other problem is taken care of. Correcting the problem will not turn the CEL off. Disconnecting the battery will not turn the CEL off.