Evaporative Emissions System: Description and Operation

GENERAL INFORMATION
The evaporative emission control system prevents the emission of fuel tank vapors into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to the charcoal filled EVAP canister. The EVAP canister temporarily holds the vapors. Through the EVAP
purge solenoid, the powertrain control module (PCM) allows intake manifold vacuum to draw vapors into the combustion chambers during certain engine operating conditions. The plunger solenoid regulates vapor flow from the canister to the engine.

OPERATION
The EVAP purge solenoid regulates the rate of vapor flow from the EVAP canister to the throttle body. The PCM controls solenoid operation. During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged. The EVAP purge solenoid operates at a frequency of 200 Hz and is controlled by an engine controller circuit that senses the current being applied to the EVAP purge solenoid and then adjusts that current to achieve the desired purge flow. The EVAP purge solenoid controls the purge rate of fuel vapors from the EVAP canister and fuel tank to the engine intake manifold.




COMPONENT LOCATION