I Have An Evaporative Emission System Leak. What Is Going On?

Whats an EVAP Leak?

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An EVAP leak is a small hole or a crack in the evaporative emissions (EVAP) system. The EVAP system is responsible for collecting and recirculating gasoline vapors from the fuel tank and preventing them from entering the atmosphere.

When there’s a leak in the system, it can cause gas vapors to escape into the air, which can be harmful to the environment and potentially dangerous to nearby people and animals.

There are a few different ways that an EVAP leak can occur. A hole or crack in the fuel tank, fuel lines, or EVAP canister could allow vapors to escape. Additionally, a faulty purge valve or vent valve could cause a leak.

If you think you may have an EVAP leak, it’s important to have your vehicle diagnosed by a mechanic as soon as possible. Depending on the location and severity of the leak, you may need repairs to your EVAP system before it can be properly inspected and repaired.

Once the issue has been addressed, you’ll want to take steps to prevent future leaks from occurring in order to protect both yourself and the environment.

If you suspect that you have an EVAP leak, be sure to contact a trusted mechanic for vehicle repairs as soon as possible. They will be able to inspect your vehicle for any signs of damage or malfunction and perform any necessary repairs so that your EVAP system functions properly once again.

To help minimize your chances of having another leak in the future, make sure you maintain your vehicle regularly and avoid driving on rough terrain or over potholes.

In addition, make sure that all fuel caps are tightly fitted to prevent vapors from escaping accidentally. With proper care, you can help reduce your chances of an evap leak and keep yourself, your loved ones, and the environment safe as well.


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Is It Safe To Drive With An EVAP Leak?

It’s technically safe to drive with a leak, but it’s absolutely not recommended. You probably won’t burst into a ball of flames while driving, but you will be exposing other people and the planet to your vehicle’s fumes. That’s not a good look.

Is An EVAP Leak Harmful?

When you have a leak in your EVAP system it will cause a check engine light to come on, but will not immediately affect your drivability. While you drive around, however, you are letting harmful fuel vapors escape into the atmosphere and adding to the greenhouse effect that is linked to global warming.

EVAP OBD2 Codes List

When the Check Engine Light is on, the car’s computer stores a code or diagnostic trouble code (DTC) in its memory. Mechanics and technicians use the OBD2 (On Board Diagnostic) codes list to diagnose problems with the devices that hook up to a car’s computer.

Here is a list of some of the most common EVAP DTCs and their meanings:

  • P0455 – EVAP system gross leak detected
  • P0456 – EVAP system very small leak detected
  • P0442 – EVAP system small leak detected
  • P0440 – EVAP system malfunction
  • P0443 – EVAP system purge control valve circuit or incorrect purge control valve flow
  • P0441 – EVAP system incorrect purge flow or flow during non-purge
  • P0446 – EVAP system vent control circuit malfunction
  • P0457 – EVAP system leak detected (fuel cap) or EVAP canister

Which Are The Available EVAP Systems?

There are different evaporative emissions control systems. These systems can be classified into five different categories:

  • Diurnal: This usually represents gasoline that evaporates because of the rise in ambient temperature.
  • Running losses: Represent gasoline that vaporizes because of the heat of the engine and exhaust system during normal operation.
  • Resting losses: Natural permeation that occurs from the fuel delivery system while not operating under ambient conditions.
  • Hot Soak: Vaporization of fuel because of the keep heat of the engine after the engine is turned off.
  • Refueling: Represents the fuel vapors that escape from the tank by the displacement of liquid fuel.

How Much Does it Cost to Repair an EVAP Leak?

The EVAP leak repair cost depends on what type of code you are facing. Replacing a broken gas cap only costs you about $10, while the price to replace an EVAP canister is much more. In fact, these canisters can often cost $200 or more just for the parts.

The best way to diagnose the fault is to use an OBDII scanner. This diagnostic tool will lead you in the right direction, showing you where to look for the leak. If you can fix the problem yourself, you can save a lot of money.

How Long Can You Drive With An Evap Leak?

Driving over Evap leaks is not as dangerous as it sounds. If your EVAP valve leaks while driving over 30-50 miles, there is a good chance that you won’t get the oil to properly fix the problem.

Can You Repair EVAP Leaks Yourself?

In most cases, repairing an EVAP leak requires the expertise and specialized tools of a trained mechanic. If you suspect that you may have an EVAP leak in your vehicle, it is best to seek diagnosis and repair from a trusted professional.

However, there are some steps you can take to prepare for your appointment with a mechanic, including gathering any relevant maintenance records or receipts as well as having your car inspected by another trusted mechanic prior to arriving at your appointment.

With proper care and attention to detail, though, you can help reduce your chances of experiencing another EVAP leak in the future and keep yourself and those around you safe from potential harm caused by leaks in this important system.

How Does The EVAP System Work?

The evaporative emission control (EVAP) system captures gasoline fumes and other emissions. When the fuel evaporates inside the gas tank, the excess vapors are transferred to the charcoal canister. They’re stored there until they can safely be transferred back to the engine to be burned with the normal air-fuel mixture.

When that’s ready to happen, a valve creates a vacuum that draws the vapors into the engine. Fresh air is also drawn in through the vents and valves to mix with the vapors for better combustion. These systems can be controlled mechanically, or like on newer cars, through the engine’s computer.

If the fuel tank was sealed tight, the fuel pump could create enough negative pressure to collapse it.

So, on older EVAP systems, the tank is vented by a spring-loaded valve inside the gas cap. While, On newer vehicles, it is vented through the EVAP canister.

It’s difficult to wrap your head around how a typical EVAP system works. But the good news is that the system’s functions can be broken down into three primary operations: storing fuel vapors, purging fuel vapors, and self-monitoring.

The EVAP system has three primary operations:

  • Storing fuel vapors.
  • Purging fuel vapors.
  • Self-monitoring.

#1. Storing Fuel Vapors

The vapor canister is the focal point of the EVAP system. When the engine is off, fuel vapors from the gas tank are stored in the canister. The canister contains activated charcoal, which traps the vapors until the engine is running, and conditions are correct for a vapor purge.

Normally, the vapor canister is open to the atmosphere to allow fresh air to enter. The canister is only closed when the EVAP monitor is run.

#2. Purging Fuel Vapors

In modern vehicles, the PCM determines when to start a canister purge. When the module deems conditions to be correct, it commands a solenoid to open the purge valve.

Opening the purge valve creates a vacuum that pulls fresh air through the vapor canister. The fresh air picks up the fuel vapors and delivers them to the engine to be burned during the normal combustion process.

#3. Monitoring For Leaks And Proper System Operation

As was mentioned, all vehicles built after 1999 have enhanced EVAP systems that can perform self-tests for both leaks and proper system operation. This test sequence is referred to as the EVAP monitor.

The monitoring strategy will vary, depending on the type of vehicle. When the conditions are correct, the control module closes the vent valve and opens the purge valve, creating a vacuum in the system.

The control module then monitors the fuel tank pressure (FTP) sensor to verify the system can reach a specified amount of vacuum.

If the vacuum is lower than specified, the module assumes there is a large leak somewhere in the system and stores a DTC in its memory.

Can Evap Purge Valve Cause Stalling?

As soon as the purge solenoid goes out, the check engine light appears, and if the emissions test comes back false, your vehicle will not pass. Additionally, the buildup of fumes during purge can cause your vehicle to stall or malfunction. A leak in the EVAP system is causing the vehicle to stall.

What should I do when I have an Evaporative Emissions Systems Leak?

There are more than 1,000 different causes of a check engine light coming on. 

The first step is to stop by a car parts store or a mechanic and have them run an OBD test on your engine. Before you walk into the store, double check to make sure your gas cap is firmly secured – save yourself the embarrassment of the mechanic calling you out right away for this!

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

If the gas cap is on correctly, there may be a more serious issue, such as a leak in the fuel system.

If your Check Engine Light comes on and you suspect a leak in your EVAP system, it is best to have a mechanic inspect the vehicle. EVAP problems 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.

Assuming that it’s a more serious case, the OBD reading should produce a code that identifies the problem. In this case, that code signifies the EVAP leak and the mechanic or parts employee can advise on the probable issue.

If you are driving when the check engine light comes on, there is a much better chance that this is the issue than if you were parked. The engine monitoring system in your car typically won’t pick up on these leaks when the car is turned off.

While the car is driving, there may be a smell or temperature change that triggers the light to go on.


Like other issues that cause the check engine light to come on, it is important that you get an evaporative emissions system leak looked at right away.

By letting it sit, you’re only making the problem worse and improving the chances of more serious damage down the line.

For the optimal life of your vehicle, important engine care is absolutely essential. Most parts stores and mechanics can fix, or sell you the materials to fix, this problem at a reasonable rate and you shouldn’t have a repeat.

If you have enjoyed this article, please give it a share on social media. Who knows – you might be saving a friend or relative from a major engine repair just be giving them this information! Have a particularly crazy story about EVAP leaks to share? Put it in the comments below and let’s get a discussion going.


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