Evaporative Emission (EVAP) System
The EVAP system consists of an EVAP leak detection control module, EVAP canister, EVAP purge valve, fuel tank, capless fuel tank filler pipe, fuel vapor vent valve (FVVV), fuel tank isolation valve (FTIV), fuel tank pressure (FTP) sensor, fuel vapor hoses, intake manifold hose assembly, and the PCM.
The fuel tank side is normally sealed by the closed FTIV and the FVVV which block the flow of vapors from the fuel tank to the EVAP canister. This system only allows fuel vapors into the EVAP canister during refueling or an excessive fuel tank pressure condition.
During the EVAP leak check monitor, the PCM controls the EVAP leak detection control module to seal the EVAP canister from the atmospheric pressure by closing the switching valve and applying the target vacuum in the EVAP system by turning ON the vacuum pump. Operation of the system is as follows:
- The FTP sensor monitors the fuel tank pressure and continuously transmits an input signal to the PCM.
- The normally closed FVVV is a PCM controlled valve that blocks the flow of vapors from the fuel tank to the EVAP canister. The PCM opens the FVVV to allow fuel vapors to the EVAP canister during refueling.
- The normally closed FTIV is a PCM controlled valve that blocks the flow of vapors from the fuel tank to the EVAP canister. The FTIV will automatically open to relieve excess pressure or vacuum if the fuel tank pressure or vacuum reaches a maximum calibrated value.
- The EVAP leak detection control module is used to seal the EVAP system from the atmosphere and apply a vacuum on the EVAP system for EVAP leak check monitoring. A vacuum pump inside the EVAP leak detection control module applies a vacuum on EVAP system as needed during the EVAP leak check monitor. The pressure sensor internal to the EVAP leak detection control module monitors the system during the EVAP leak check monitor.
- The EVAP purge valve is used to control the purge flow from the EVAP canister during engine running conditions.
- The EVAP canister is used on the sealed EVAP system to collect fuel vapors during refueling only.
- A valve inside the fuel tank mounted fuel vapor tube assembly prevents liquid fuel from entering the EVAP canister and the EVAP purge valve under any vehicle altitude, handling, or rollover condition.
Typical EVAP System