Schematic Diagram

Canister: The canister is filled with charcoal and absorbs evaporated fuel vapor from the fuel tank. The fuel vapor collected in the canister is drawn into the intake manifold by the ECM/PCM when the appropriate conditions are met. Purge Control Solenoid Valve (PCSV): The PCSV is installed in the passage connecting the canister and the intake manifold. It is a normally closed solenoid valve controlled by a signal from the ECM/PCM. To draw the absorbed vapor into the intake manifold, the ECM/PCM opens the PCSV; otherwise, the passage remains closed. Fuel Tank Cap: The ratchet tightening device on the fuel tank cap reduces the likelihood of incorrect installation and sealing of the filler neck. When the gasket on the fuel tank cap and the filler neck flange make contact, the ratchet produces an audible click, indicating that the cap is properly installed. Fuel Tank Pressure Sensor (FTPS): The FTPS is an integral part of the monitoring system. The FTPS checks the operation of the purge control solenoid valve (PCSV) and detects leaks in the evaporative emission control system by monitoring the pressure and vacuum level in the fuel tank during PCSV operating cycles. Canister Close Valve (CCV): The CCV is located between the canister and the fuel tank air filter. It closes the air inlet to the canister for the evaporative emission system and prevents fuel vapor from escaping from the canister when the vehicle is not operating. EVAP System Monitoring: The evaporative emission control system monitoring consists of a fuel vapor generation stage, a vacuum stage, and a leak check stage. First, the OBD-II system checks whether vapor generation due to fuel temperature is low enough to start monitoring. Then the evaporative system is evacuated through the PCSV with a ramp to maintain a specific vacuum level. The final stage checks for vacuum loss due to any leaks in the system. Vapor Generation Check: During the stabilization period, the PCSV and CCV are closed. The system pressure is measured as the initial pressure (DP_A). After a specified period (T1), the system pressure is measured again (DP_B) and the difference from the initial pressure is calculated. If this difference (DP_B - DP_A) is greater than the threshold value, there is excessive vapor and the monitor is aborted for the next check. Conversely, if the difference is less than another negative threshold, the PCSV is judged to be faulty, such as stuck open. Evacuation: The PCSV opens with a specified ramp to reduce the pressure to a specific level. If the pressure cannot be reduced below the threshold, the system is judged to have a loose fuel cap or a large leak. Leak Check: The PCSV closes, and the system waits for some time for the pressure to stabilize. During the check period (T2), the system measures the start and end pressures (DP_C, DP_D). The diagnostic value is the pressure difference corrected for the natural vapor generation rate (DP_B - DP_A) from the vapor generation check step.