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.

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.

Evaporative Emission Purge Control Valve And Solenoid

Consequently, A typical system consists of:

  • A small canister full of charcoal
  • Valves
  • Hoses
  • Vents in the fuel lines
  • 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.

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

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.

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

As a result, The canister purge valve controls the flow of these vapors. The valve regulates when and how much of these vapours enter your engine. Another name for the canister purge valve is the solenoid.

Check Engine Light Is On

So, The first sign of trouble for your canister purge valve is the check engine light coming on. If your car’s computer detects higher or lower than expected purging from the valve; it will illuminate the check engine light. Probably, setting off error codes as well.

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

  • So, 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. Consequently, this enriches the fuel mixture and will likely foul the spark plugs. Also, Most charcoal canisters have a filter that should be replaced periodically.

Evaporative Emission Charcoal Canister

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. Also, When the engine is running, a purge valve opens, allowing vacuum to siphon the fuel vapors into the engine.

So, Fixing (EVAP) codes can be a challenge, even for professional technicians. Finally, If you have a P0442 small leak code, you’ll probably have to use a smoke machine to find it.

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