The gas cap is a very simple, but important component that is found on the vast majority of road going vehicles. It’s purpose is to ensure that no dirt, debris, or dust enter your fuel tank, and that none of the fuel vapors escape. The gas cap plays an important role in the proper operation of the vehicle’s evaporative emissions system, which is designed to trap and reuse fuel vapors that would otherwise be released into the atmosphere. As the gas cap is removed every time the vehicle is refueled, it will often wear out simply due to repeated use. While a faulty gas cap will not necessarily cause major performance issues, it can cause the vehicle to experience fuel and emission problems. Usually a bad or failing gas cap will produce a few symptoms that can alert the driver of a potential problem.
1. Cap does not tighten properly
One of the first symptoms of a bad or failing gas cap is a cap that does not tighten properly. Most fuel caps have a built in mechanism that will cause them to click once they are adequately tightened. If when tightening the cap, it does not eventually click, or pops loose after it clicks then that is a sign that the cap may be damaged and need to be replaced.
2. Fuel smell from the vehicle
Another symptom of an issue with the fuel cap is a fuel smell from the vehicle. If the gas cap leaks, or fails to provide a proper seal it can cause fuel vapors to escape from the fuel tank, which may cause the vehicle to give off a fuel smell. A fuel smell can also be caused by various other issues, so a proper diagnosis is recommended if you are unsure.
3. Check Engine Light comes on
Another common symptom of an issue with the fuel cap is an illuminated Check Engine Light. If the fuel cap has any issues sealing the fuel tank it can cause the Check Engine Light to come on for evaporative emissions system reasons. The vehicle’s evaporative emissions system is designed to trap and reuse fuel vapors, and can detect if there is a leak in the system. A leaky fuel cap will compromise the effectiveness of the evaporative emissions system, and as a result will set off the Check Engine Light to notify the driver of the issue. A Check Engine Light can also be set off by a wide variety of other issue so having the computer scanned for trouble codes is highly recommended.
While a faulty fuel cap probably won’t cause any major drivability issues with the vehicle, it can cause the Check Engine Light to illuminate. If you suspect that your gas cap may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if the cap should be replaced.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Fuel Filler Cap and was authored by Eduardo Ruelas.