EVAP Leak Check Monitor

The EVAP system is a sealed system by the use of the normally closed fuel tank isolation valve (FTIV) and the normally closed fuel vapor vent valve (FVVV). If the natural vapor pressure or vacuum generation in the sealed fuel tank is sufficient the PCM will command the EVAP leak detection control module to check the FTIV, the FVVV, the EVAP purge valve, the switching valve in the EVAP leak detection control module and the lines between those components. The fuel tank pressure (FTP) sensor monitors the sealed portion of the EVAP system between the FTIV, the FVVV and the capless fuel filler pipe to determine the total pressure or vacuum in the fuel tank. If the target pressure or vacuum has been reached the fuel tank side is considered to have no leak. If the sealed portion of the EVAP system does not generate enough pressure or vacuum between the FTIV, the FVVV and the capless fuel filler pipe then the PCM will open the FTIV and will turn ON the EVAP leak detection control module vacuum pump to apply vacuum to the entire EVAP system.

The EVAP leak check monitor is initiated at ignition OFF if the conditions to run the monitor have been met during the preceding drive cycle. The EVAP leak check monitor is executed by using the individual components of the enhanced EVAP system as follows:

1. The FTP sensor is used to determine if the target pressure or vacuum necessary to carry out the leak check on the sealed fuel tank has been reached.
2. The FVVV is a PCM controlled valve that blocks the flow of vapors from the fuel tank to the EVAP canister. The FVVV is normally closed to prevent the canister from becoming saturated in a situation where the engine does not run during a drive cycle, causing hydrocarbons (HC) to be released into the atmosphere. The PCM will open the FVVV for refueling.
3. The FTIV is a PCM controlled valve that blocks the flow of vapors from the fuel tank to the EVAP canister. The FTIV is normally closed to prevent the canister from becoming saturated in a situation where the engine does not run during a drive cycle, causing hydrocarbons (HC) to be released into the atmosphere. The FTIV will automatically open if the fuel tank pressure or vacuum reaches a calibrated value. The PCM will open the FTIV only if the sealed section of the EVAP system does not generate enough pressure or vacuum to complete the EVAP leak check monitor.
4. The EVAP leak detection control module is used to seal the EVAP system from the atmosphere and draw a vacuum on the EVAP system for leak check monitoring. A vacuum pump inside the EVAP leak detection control module draws a vacuum on either the canister side of the EVAP system or on the entire EVAP system as needed. If the initial target vacuum cannot be reached, a leak is detected and a DTC will set. The EVAP leak detection control module internal components are tested during the EVAP leak check monitor. A DTC will be set if a concern is detected with the internal EVAP leak detection control module components.
5. The EVAP purge valve is used to control the purge flow from the EVAP canister during engine running conditions.
6. The EVAP canister is used on the sealed EVAP system to collect fuel vapors during refueling only.
7. A valve inside the 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.

   Courtesy of FORD MOTOR CO.

   EVAP Leak Check Monitor