When it is open, the ECM monitors the vapor pressure in the charcoal canister. When the VSV for vapor pressure sensor is closed, the ECM monitors the vapor pressure in the fuel tank. This diagnostic checks the function of the EVAP VSV and VSV for vapor pressure sensor, the integrity of these components and the fuel tank from the standpoint of fuel vapor emissions. The ECM uses the vapor pressure sensor to detect malfunctions in the evaporative emissions (EVAP) system. The ECM controls a duty–cycle type VSV (vacuum switching valve) to purge evaporative emissions from the charcoal canister. The EVAP control system is a system which utilizes the intake manifold vacuum to draw the evaporative emissions into the intake manifold and mix them with intake air. If the ECM does not detect any change in the engine RPM or the air/fuel ratio when opening the EVAP VSV, the ECM will determine that there is a malfunction of the EVAP VSV and set a DTC. The ECM monitors both of the engine RPM and the air/fuel ratio for this EVAP system diagnostic test. When the EVAP VSV is opened, the engine speed and the air/fuel ratio should change. The ECM controls a duty–cycle type VSV (vacuum switching valve) to purge the evaporative emissions from the charcoal canister.ĮVAP VSV Monitor (DTC P0441, im3) The ECM controls the opening and closing of the EVAP VSV (vacuum switching valve). The old EVAP control system is a system which utilizes the intake manifold vacuum to draw the evaporative emissions into the intake manifold and mix then in with the intake air. When operating conditions can tolerate additional enrichment, these stored fuel vapors are purged into the intake manifold and added to the incoming air/fuel mixture. It is then transferred to the EVAP system charcoal canister when tank vapor pressures become excessive. Fuel vapor is normally created in the fuel tank as a result of evaporation. The EVAP system is a fully closed system designed to maintain stable fuel tank pressures without allowing fuel vapors to escape to the atmosphere. Improper operation of the EVAP system may cause rich driveability problems, as well as failure of the Two Speed Idle test or Enhanced I/M evaporative pressure or purge test.
This fuel charge is added during periods of closed loop operation when the additional enrichment can be managed by the closed loop fuel control system. The EVAP system delivers these vapors to the intake manifold to be burned with the normal air/fuel mixture.
The Evaporative Emission Control (EVAP) System is designed to store and dispose of fuel vapors normally created in the fuel system thereby, preventing its escape to the atmosphere. Charcoal canister (EVAP System) Charcoal canister (EVAP System) Evaporative Emission Control System (DTC P0440, P0441, P442, P0446, P0450, P0451, etc)Īpproximately 20%of all hydrocarbon (HC) emissions from the automobile originate from evaporative sources.
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