There are many reasons the owner of a Mercedes C240 might need to replace the car's gas cap. A faulty gas cap is a common cause of emissions control system failure, or the cap may have been lost or stolen. You can save money by replacing the cap yourself instead of taking the car to a dealership or repair shop. On a Mercedes C240, a retaining strap holds the gas cap while you refuel this luxury car.
Park the Mercedes C240 on level ground with the parking brake set and the ignition off.
Open the external fuel door to reveal the gas cap.
Unscrew the cap as you would if you were going to refuel the car.
Remove the screw attaching the gas cap retaining strap to the Mercedes C240's body, using the Phillips screwdriver.
Attach the new cap's retaining strap to the car body, using the screwdriver and the screw that held the old cap's retaining strap.
Screw the cap into place as you would after refueling the car and close the external fuel door.
