Instead, your EVAP system creates a sealed system that channels your fuel vapors through a series of hoses into a charcoal filter canister. Without a proper seal, these vapors could easily escape. While your vehicle is at rest, vapors are being released from your fuel tank. OBD II Enhanced EVAP systems contain a vent valve.Your vehicle’s EVAP system helps reduce your emissions and prevent harmful fuel vapor leaks into the environment. The ECM also uses it to monitor purge valve operation. Vent Valve: The vent allows fresh air to enter the canister. This input, along with other sensor inputs, determines if there is a fault in the tank's seal.
A faulty purge solenoid can result in a rough idle and difficulty starting.įuel Tank Pressure Sensor: This is an input used by the ECM to indicate if the system is leaking into the atmosphere. The ECM purges the system only after meeting certain conditions like engine temperature and speed. Purge Solenoid: The purge solenoid is responsible for venting the tank's fuel vapor into the intake manifold. The ECM typically purges the canister in gear after the engine has warmed and reached a specific temperature. Late-model vehicles have an enhanced evaporative system equipped with a canister located close to the tank to capture fuel vapor during refueling.
Enhanced EVAP systems found on today's vehicles are computerized and typically diagnosed with a visual inspection, a multimeter, and a scan tool.Ĭharcoal Canister: The canister contains a charcoal insert that absorbs and retains fuel vapor until it's purged into the intake manifold for combustion. The basic systems installed on these early model vehicles were uncomplicated and vacuum controlled.
Evaporative emissions were installed on vehicles in the late 1960s when they realized that 10-20% of the vehicle's hydrocarbon emissions occurred while the vehicle sat at rest.
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