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You’re driving when you notice the Check Engine warning light come to life in your instrument panel. At about the same time, you smell gas right inside the cabin of your car. It may be a really faint smell, but you smell it nonetheless. Immediately you’re concerned. Is there something wrong with your car? A quick search on the internet using your smartphone will tell you that you might have an EVAP leak in your hands. But the real question is if it is safe for you to keep driving?

Is it Still Safe to Drive Even with a Leak in the EVAP System?

The short answer is, ‘yes’. However, this doesn’t mean that you should. The EVAP system in your car serves to contain the fumes that are created by fuel in your tank. These fumes have to be prevented from getting into the atmosphere so that they will not contribute to the already-worsening air pollution. So, yes, you can still drive your vehicle safely as it really doesn’t have a bearing on the overall performance of your car. Unfortunately, as we already mentioned, you will be releasing gas fumes into the atmosphere which other individuals may inhale.

A Closer Look at the EVAP System

Every time we gas up we are putting a variety of chemicals into our fuel tank including benzene and toluene, and to some extent, lead. These 150 or so chemicals can make people dizzy, experience breathing difficulties, or even have headaches when the fumes these chemicals create are inhaled. Gasoline that has evaporated into the atmosphere is also one of the planet’s leading causes of air pollution and smog.

In the 1970s, the EPA started implementing measures to help curb gasoline evaporations. As such, some vehicle manufacturers have begun installing evaporative emission control systems or EVAP systems in their cars. EVAP systems are primarily intended as a miniature storage facility for the vapors of fumes from gasoline so that these do not escape into the environment.

Depending on the design of the EVAP system, these can include a small canister that contains charcoal which effectively absorbs and neutralizes the fumes. The gasoline fumes are stored in this charcoal canister until they are deemed safe to be reused in the car’s fuel system. These vapors are drawn to the engine through a valve that creates a powerful suction. Additional valves and vents allow fresh air to mix with the gasoline vapors before these are directed to the intake valve of the engine. These can also lead to better combustion.

Controlling the EVAP system can be achieved mechanically or, in the case of modern cars, electronically via computer. The computer in the car tells the system when to purge the charcoal canisters containing the gasoline vapors. The purging of the EVAP system’s canisters typically occur while the vehicle is in motion to help in the optimum operation of the engine.

It is for this reason that a problem in the EVAP system almost always coincides with the emergence of signs or symptoms while you’re driving and not when the vehicle is idle.

Why There Can Be Leaks

A leak in the EVAP system can occur almost anywhere. It can be because of damage to the hoses that convey the gasoline fumes to the engine. As everyone knows, hoses are not exactly immune from damage. Over time, they can become brittle and form cracks where fumes can escape. It is also possible that one of the EVAP hoses has been disconnected, allowing the vapors to escape.

Another potential cause of a leak in the EVAP system is leaks in the charcoal canister itself. Again, these can degrade over time because of corrosion or exposure to impact forces. The canister itself can get cracked allowing vapors to hiss through the small opening. The canister can get severely damaged that your only recourse is to have it replaced.

Other causes of EVAP leaks can include faulty vent control valve or the purge valve. These valves can get stuck in their respective openings, too. When stuck, they will not be able to function normally and will not be able to purge the stored gas vapors into the engine’s intake valve. It is also possible that there’s a problem in the leak detection pump or any other leak in the car’s fuel system.

But the most common – and most often overlooked – cause of EVAP leaks is a damaged or loose gas cap. As always, this device can be subject to wear and tear with the passing of time. Or you simply failed to tighten it well or to close it all the way such that vapors can still escape.

Symptoms of an EVAP Leak

The Check Engine light is the most common indicator of an EVAP leak. Unfortunately, this is not the only reason why you may have the Check Engine warning light blinking in your dashboard. As such, it should always be considered in the presence of other symptoms, the most striking of which is the unmistakable odor of gasoline getting inside the passenger cabin. If this occurs while you’re driving and the Check Engine light turns on and starts to blink, then there is a very high likelihood that you have an EVAP leak.

During normal engine operation, the car’s engine computer module keeps track of the pressure inside the EVAP system. If there is a leak, usually caused by a loose or badly damaged gas cap, it triggers an event which activates the Check Engine light in the instrument panel.

One of the most commonly overlooked symptom of an EVAP leak is a reduction in gas mileage. Gasoline is very volatile. It can easily turn into a gaseous state within minutes. And if you have a leak in the EVAP system the rate of evaporation can also be increased, leading to a significant reduction in fuel economy.

While it is perfectly safe to drive even though there is a leak in the EVAP system, you are essentially exposing other people to these noxious fumes. It’s bad for the environment and, in the long run, not good for your wallet, too. Have your system checked as soon as possible.

Source:

  1. How Evaporative Emission Control Systems Work – howstuffworks
  2. Is it Safe to Drive With an EVAP Leak? – YourMechanic

 

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