Circuit Description

The Evaporative Emission (EVAP) control system prevents emission of fuel vapors. Fuel vapor generated in fuel tank while driving or idling enters EVAP canister where a charcoal element absorbs and stores the fuel vapor. When certain engine operating conditions are met, PCM purges EVAP canister of stored vapors by turning on the EVAP canister purge valve. Emissions laws require that PCM detect any leakage within the EVAP system. PCM monitors Fuel Tank Pressure (FTP) sensor in order to detect any abnormalities within the EVAP system. PCM supplies a 5-volt reference voltage, a sensor ground and an input signal circuit to FTP sensor.

DTC will set when engine is idling, no vehicle speed is detected and EVAP pressure switching solenoid is off. DTC will also set when FTP sensor output voltage rapidly shifts from inside to outside a specified range.