Evaporative Emissions System: Description and Operation

System Diagram:

EVAP Control System Outline
The EVAP control system prevents fuel vapor from releasing to the atmosphere and consists of the following:
- Purge control system
- On-board refueling vapor recovery (ORVR) system
- EVAP control system monitor

Purge Control System Outline
- Fuel vapor is stored in the charcoal canister until it is purged to the engine for burning.
- The PCM sends a duty signal to the purge solenoid valve to control the purge amount.
- The purge amount is determined based on the signal from the following sensors:
- Purging take place during a preset period after starting the engine. Purging can take place during idle.

Block Diagram:

On-Board Refueling Vapor Recovery (ORVR) System Outline
- The pressure control valve maintains fuel vapor passage to the charcoal canister during refueling.
- Fuel vapor during refueling is stored in the charcoal canister.

Monitoring Condition:

EVAP Control System Monitor Outline
- The system is monitored one time per drive cycle.
- The canister drain cut valve (CDCV) seals the system from atmosphere to monitor leakage, blockage and proper operation of individual components. The fuel tank pressure sensor (FTP) signal is used to determine a malfunction.
- The CDCV, purge solenoid valve and fuel tank pressure sensor circuits are also checked by the PCM.

EVAP Control System Component Part Description
Fuel shut-off valve
- The valve has a spring supported float which prevents liquid fuel from flowing to the charcoal canister during tight turns and vehicle rollover.
- The valve releases fuel vapor to the charcoal canister.
- The valve prevents the fuel tank from overfilling during refueling.

Rollover valve
- The valve has a spring supported float which prevents liquid fuel from flowing to the charcoal canister during tight turns and vehicle rollover.

Charcoal canister
- The charcoal canister stores fuel vapor from the fuel tank.
- The charcoal canister contains active carbon.

Purge solenoid valve
- The valve is normal-close type.
- The PCM sends a duty signal to the valve to control the fuel vapor purge amount.

CDCV
- The CDCV is normal open type.
- The CDCV is used during EVAP control system monitoring and seals the EVAP control system from atmosphere.


Fuel tank pressure (FTP) sensor




- The FTP sensor converts the fuel tank pressure into a voltage value and sends the voltage signal to the PCM.