An EVAP leak is a fault in the evaporative emission control system (EVAP). The EVAP’s function is to keep gas fumes in the gasoline tank from reaching the atmosphere. This keeps air pollution down, and keeps the smell of fuel from reaching the inside of your vehicle. Some symptoms that will let you know that there is an issue with the EVAP system:

  • One symptom of an EVAP leak is the Check Engine Light coming on while you are driving. A slight fuel odor may also be noticed, but it does not happen in all vehicles. If your Check Engine Light does come on, and you just filled your gas tank up, check the gas cap.

  • The most common cause of an EVAP leak warning, or the Check Engine Light, is the gas cap not being closed properly. If the cap is not fully tightened or closed all the way, the Check Engine Light may come on. Before taking your vehicle to the mechanic, check your gas cap to make sure it is positioned on the tank correctly and closed tightly.

  • If the gas cap is on correctly, there may be a more serious issue, such as a leak in the hose system. Other issues could be a faulty vent o-ring seal, defective leak detection pump, defective purge valve, or another small leak in the EVAP system.

  • Fuel vapors emit from the vehicle any time there is gasoline in the tank. So if you have a leak, even if you are not driving the vehicle, those vapors are polluting the air 24 hours a day. Uncontrolled emissions like this account for about 20 percent of the pollution produced by vehicles.

  • If your Check Engine Light does come on and you suspect a leak in your EVAP system, it is best to have a mechanic look at the vehicle. EVAP codes can be challenging and the mechanic will have to use advanced troubleshooting techniques to determine where the leak is, as well as how severe it is.

While it is safe to drive with an EVAP leak, you should not drive your vehicle for long while you do have a leak. If your Check Engine Light comes on, check to make sure the gas cap on your vehicle is securely fastened. If the light is still on, take it to a mechanic so the leak can be fixed. It takes a professional to troubleshoot and repair an EVAP leak.

This article originally appeared on YourMechanic.com as Is it Safe to Drive With an EVAP Leak? and was authored by Valerie Johnston.


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