Evaporative Emission Control System (EVAP) – Traps Emissions

Evaporative Emission Control System (EVAP)
Evaporative Emission Control System (EVAP)

The function of the Evaporative Emission Control System (EVAP) is to trap and store evaporative fuel emissions.

The EVAP system therefore, totally eliminates fuel vapors as a source of air pollution.

So, Sealing the fuel tank is not as simple as it sounds.

For one thing, a fuel tank must have some type of venting so air can enter to replace the consumed fuel.

The evaporative emission control (EVAP) system captures gasoline fumes and other emissions.

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.

Consequently, A typical system consists of a small canister full of charcoal, valves, hoses, vents in the fuel lines and a sealed fuel tank cap.

When 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.

The most obvious symptom of an EVAP system problem is the Check Engine light. A common cause of this is a loose gas cap. Finally, If you’ve recently filled up on fuel, check that the gas cap is fully tightened.

Consequently, If the Check Engine light remains on after checking the gas cap, there may be a bigger problem.

Evaporative Emission Control System (EVAP) Components:

  • Fuel Tank
  • Fuel Cap
  • Liquid-Vapor Separator
  • EVAP Canister

Common Problems-Evaporative Emission

All EVAP systems have a charcoal canister that it relies on. The canister has a huge surface area that is effective in storing vapors from the fuel. If the charcoal canister were to go bad, there would be an array of problems. In addition, to power reduction, fuel odor, more pinging, lower fuel economy, and flooding.

So, most common problems with the EVAP system include faults with the purge valve that vents fuel vapors to the engine. The canister purge valve, also commonly referred to as the purge valve, is an important component of your (EVAP) system. So, This system restricts the fuel vapours created in your fuel tank from escaping into the atmosphere by trapping them. When your engine runs at regular speed, the EVAP system slowly allows these vapours to be released into your engine.

Purge Valve
Purge Valve

The flow of these vapours is controlled by your canister purge valve. The valve regulates when and how much of these vapours enter your engine. The canister purge valve is electrically operated, and is also referred to commonly as a solenoid. The most common purge valve issues are when the purge valve is stuck open or closed. Also, It may just not open at the proper time. The symptoms are listed below that may indicate your canister purge valve is not functioning properly.

Check Engine Light Is On

  • The first sign of trouble for your canister purge valve is the check engine light coming on. Consequently, Your canister purge valve is controlled by your car’s computer, which allows it to monitor its performance. If your car’s computer detects higher or lower than expected purging from the valve, it will illuminate the check engine light.  Common error codes include P0441 and P0446, as well as other EVAP codes.

Purge Valve Stuck Closed

  • Furthermore, If your canister purge valve is not opening properly, it may adversely impact your gas mileage. So, The reason for this is that the vapours that your car regularly uses will be vented to the environment. Finally, You will lose a portion of the fuel regularly used in burning.

Purge Valve Stuck Open

  • If your canister purge valve is stuck open it creates a vacuum leak that can affect your engine adversely. Simply put, air will be allowed to enter the engine in a quantity that is not predicted by your computer. This will change the car’s air to fuel ratio, and can cause rough idling, as well as difficulty starting. Therefore, If experienced together, there is a high likelihood of a failing canister valve. As a result, this enriches the fuel mixture and will likely foul the spark plugs. Also, Most charcoal canisters have a filter that should be replaced periodically.

Possible Fault Codes-Evaporative Emission Control System (EVAP):

  • P0440….Evaporative Emission Control System Fault
  • P0441….Evaporative Emission Control System Incorrect Purge Flow
  • P0442….EVAP Emission Control System Leak Detected (small leak)
  • P0443….EVAP Emission Control System Purge Control Valve Circuit
  • P0444….EVAP Purge Control Valve Circuit Open
  • P0445….EVAP Purge Control Valve Circuit Shorted
  • P0446….Evaporative Emission Control System Vent Control Circuit
  • P0447….EVAP Emission Control System Vent Control Circuit Open
  • P0448….EVAP Emission Control System Vent Control Circuit Shorted
  • P0449….EVAP Emission Control System Vent Valve/Solenoid Circuit
  • P0450….Evaporative Emission Control System Pressure Sensor
  • P0451….EVAP Emission Control System Pressure Sensor
  • P0452….EVAP Emission Control System Pressure Sensor Low Input
  • P0453….EVAP Emission Control System Pressure Sensor High input
  • P0454….EVAP Emission Control System Pressure Sensor Intermittent
  • P0455….EVAP Emission Control System Leak Detected (gross leak)
  • P0456….EVAP Emission Control System Leak Detected (small leak)
  • P0457….EVAP Emission Control System Leak Detected (fuel cap)


Consequently, 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. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

So, Fixing EVAP codes can be a challenge, even for professional technicians. In conclusion, If you have a P0442 small leak code, you’ll probably have to take your car to a repair shop that has a smoke machine.

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