Q: Check engine light came on in my 2001 Toyota Avalon after getting gas. Have heard this can be a gas cap problem

You’re right, this could be a gas cap problem. But it could also be any number of other problems. The check engine light comes on whenever the computer detects a fault in the car’s emissions systems and the computer stores trouble codes that can help a technician figure out what the problem is. The light will not go out just because a fault has been corrected until it has been reset by a scanner or until the computer sees a number of drive cycles (I think it’s 50) without seeing the fault again. Disconnecting the battery will not do the trick and may lead to other issues. You need to resist the temptation to start replacing parts until you know what is really wrong. Having the computer scanned and knowing what the trouble codes really are is your best next step. You can have that conveniently done by contacting YourMechanic. They can send a technician to your home or office to read and interpret your trouble codes and let you know what to do next.