The EVAP canister vent valve is an integral part of the EVAP vacuum leak pump
assembly (2). The vent valve controls the flow of clean air into or out of (3)
the EVAP canister. The vent valve is normally open. Under certain conditions the PCM
commands the vent valve closed in order to seal the EVAP system for leak diagnosis.
The fuel tank pressure (FTP) sensor, measures the difference between the fuel
tank and outside air pressure. The FTP sensor is an integral part of the EVAP vacuum
leak pump assembly. The PCM provides a 5-volt reference and a ground to the
FTP sensor. The FTP sensor provides a signal voltage back to the PCM that can vary
between 0.1 and 4.9 volts. As the fuel tank pressure increases, the FTP sensor voltage
decreases, as the fuel tank pressure decreases the FTP sensor voltage increases.
High pressure = high voltage. Low pressure vacuum = low voltage.
The EVAP filter (1) is attached to the EVAP canister and provides clean
air for the purging of fuel vapors. Excess pressure in the EVAP system also flows
thru the EVAP filter and is released into the atmosphere. The filter element is a
sealed unit and is not serviceable separately.
The EVAP service port is located underhood in the EVAP purge line, between the
EVAP purge solenoid valve and the EVAP canister. The service port is identified by
a green colored cap.