Evaporative Emission Control System

Canister
canister is filled with charcoal and absorbs evaporated vaporin fuel tank. The gathered fuel vapor in canister is drawn into the intake manifold by the ECM when appropriate conditions are set.
Purge Control Solenoid Valve (PCSV)
Purge Control Solenoid Valve (PCSV) is installed in the passage connecting canister and intake manifold. It is a duty type solenoid valve and is operated by ECM signal.To draw the absorbed vapor into the intake manifold, the ECM will open the PCSV, otherwise the passage remains closed.
Canister Close Valve (CCV)
The Canister Close Valve (CCV) is located between canister and fuel tank air filter. It closes off the air inlet to the canister for the Evaporative Emissions System leak detection inspection function and also prevents fuel vapors from escaping from the Canister when the vehicle is not operating.
Fuel Tank Pressure Sensor (FTPS)
The Fuel Tank Pressure Sensor (FTPS) is an integral part of the monitoring system. The FTPS checks Purge Control Solenoid Valve (PCSV) operation and leaks in the Evaporative Emission Control System by monitoring pressure and vacuum level in the fuel tank during PCSV operating cycles.
Fuel Filler Cap
A ratchet tightening device on the threaded fuel filler cap reduces the chances of incorrect installation, which would seal the fuel filler. After the gasket on the fuel filler cap and the fill neck flange contact each other, the ratchet produces a loud clicking noise indicating the seal has been set.
Evaporative System Monitoring
Evaporative Emission Control Monitoring System consistsof fuel vapor generation, evacuation, and leakage checkstep. At first, the OBD-II system checks if vapor generationdue to fuel temperature is small enough to start monitoring,and then it evacuates the evaporative system bymeans of PCSV with ramp in order to maintain a certain vacuum level. The final step is to check if there is vacuum loss by any leakage of the system.
Vapor Generation Checking
During stabilization period, the PCSV and the CCV areclosed, and the system pressure is measured as startingpressure (DP_A). After a certain defined period (T1), the system pressure (DP_B) is measured again and the differencefrom the starting pressure is calculated. If this difference(DP_B - DP_A) is bigger than a threshold, thereshould be excessive vapor and the monitor is aborted fornext checking. On the contrary, if the difference is lowerthan another negative threshold, PCSV is regarded asmalfunction such as clogged at open position.
Evacuation
PCSV is opened with a certain ramp for the pressure toreach down to a certain level. If pressure can't be loweredbelow a threshold, the system is regarded as fuelcap-opened or having a large leakage.
Leakage Checking
PCSV is closed and the system waits for a period toget stabilized pressure. During checking period (T2),the system measures the beginning and the end of thesystem pressure(DP_C, DP_D). The diagnosis valueis the pressure difference corrected by natural vapor generation(DP_B - DP_A) rate from the vapor generationchecking step.