Evap system – What is it?

What is an evap leak

An EVAP leak is a fault in the evaporative emission control system (EVAP). It means a leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle’s fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. This keeps air pollution down and keeps the smell of fuel from reaching the inside of your vehicle

In the golden age of automotive manufacturing, engineers didn’t need to concern themselves with trivial design aspects such as containing fuel vapor. Evaporating fuel from the gas tank was simply vented to the atmosphere. Then along came the 1970s, bringing bell bottoms and the first steps toward environmental control systems. We were just figuring out that evaporated fuel was not so good for the environment. Hence the need for modern designs to capture, store and redistribute fuel vapor.

So we have the evaporative emission control system (EVAP) while the engine is running, and under predetermined circumstances, the stored, evaporated vapor is moved from the charcoal canister back to be slowly burned by the engine. This is called the purge system. Multiple sensors monitor the purge system as well as looking for leaks. There are large leaks such as a loose gas cap and there are small leaks such as a cracked canister or delivery hose.

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.

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

Why should I fix it

There are municipalities that require your car pass emission testing and even if you’re not required to pass testing there are the safety reasons for getting the leak fixed the vapors can and do get inside the car which can make you sick

Fuel vapors are emitted 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.

Is my car safe to drive with an evap leak

While it is safe to drive with an EVAP leak, you should get the leak repaired right away. If your Check Engine Light comes on, check to make sure the gas cap on your vehicle is securely fastened. If that doesn’t solve the problem, contact a shop or a mobile technician to inspect the EVAP system. It takes a professional to troubleshoot and repair an EVAP leak. 


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