Circuit Description

PCM monitors positive or negative pressure in fuel tank using fuel tank pressure sensor. Under certain engine operating conditions, PCM turns on EVAP pressure switching solenoid in order to control pressure in EVAP system. PCM is able to detect any abnormal conditions by fluctuation of this pressure. The diagnostics performed by the fuel tank pressure sensor can warn driver of a malfunction in EVAP system by illuminating the MIL. The EVAP control system prevents emission of fuel vapors. The fuel vapor generated in fuel tank while driving or idling enters EVAP canister where a charcoal element absorbs and stores fuel vapor. The EVAP canister is purged by PCM controlled EVAP canister purge valve. The EVAP canister purge valve releases fuel vapors into intake manifold to be burned in combustion process.

DTC will set when pressure indicated in EVAP canister does not drop when EVAP canister purge valve is on or when pressure indicated in EVAP canister remains very low when compared to atmospheric pressure when EVAP canister purge solenoid valve is off.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of diagnostic failure and store information in freeze frame buffer.