Theory of Operation

Evaporative systems are not new to the automotive industry. The first systems were introduced in the industry in the 1970's as a part of the overall scheme to reduce vehicle hydrocarbon emissions. They have not changed appreciably until government mandates as part of OBD II diagnostics and tightening emission regulations.

Enhanced EVAP systems are designed to reduce emissions from fuel system:
^ While vehicle is operating or parked by continually monitoring system for leaks and to activate the Service Engine Soon lamp if a problem is detected.

The ECM monitors control circuits to vent and purge solenoids and tank pressure circuitry for possible faults. As required by law, the diagnostic routine must be able to detect a leak as small as 0.040 inches in diameter. The integrity of the entire vapor handling portion of the fuel system, including the purge solenoid, purge lines, fuel tank, EVAP canister, vent line, vent solenoid, fuel filler pipe and fuel cap is continually tested.