The gas cap, also known as the fuel filler cap, is a simple but important component that is found on the vast majority of road going cars and trucks. Their purpose is simple; to prevent dirt, debris, and dust from entering the gas tank, as well as providing a reliable seal. The cap also plays an important role in the operation of the vehicle’s evaporative emissions system, which is designed to capture and reuse fuel vapors from the gas tank that would otherwise be released into the atmosphere. Because the cap is frequently removed, every time fuel is added to the vehicle, it can wear out over time and will need to be replaced. Usually a bad or failing gas cap will produce a few symptoms that can alert the driver of a potential issue.
1. Cap does not tighten properly
One of the most common symptoms of an issue with the gas cap is a cap that does not tighten properly. Most gas caps are designed to click once they are tightened sufficiently. If the cap does not click, or clicks and then pops loose again then that may be a sign that it may need to be replaced.
2. Fuel smell from the vehicle
Another symptom of a possible issue with the fuel cap is a fuel smell from the vehicle. If the gas cap seal becomes damaged or worn it may cause fuel vapors from the gas tank to leak from the filler neck. This may result in a gasoline odor from the vehicle as a result of the escaping vapors.
3. Check Engine Light comes on
An illuminated Check Engine Light is another symptom of a potential issue with the vehicle’s gas cap. The gas cap is a part of the vehicle’s evaporative emissions system and can cause problems with the system if it has an issue. An improperly sealing fuel cap may cause an evap system leak, which will set off the Check Engine Light when the the computer detects the leak. The 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.
A bad or failing fuel cap will not necessarily cause major performance issues, but it can set off the Check Engine Light, which will prevent the vehicle from passing an emissions test. 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 Gas Cap and was authored by Eduardo Ruelas.