Circuit Description

This DTC tests EVAP system for a small leak. PCM monitors Fuel Tank Pressure (FTP) sensor signal to determine vacuum decay rate. At an appropriate time, PCM turns EVAP canister purge valve on and EVAP vent valve on. This allows engine to draw a vacuum on EVAP system. At a calibrated time, or vacuum level, PCM turns EVAP canister purge valve off, sealing the system, and monitors FTP sensor input in order to determine EVAP system vacuum decay. If PCM detects a leak larger than a calibrated amount, DTC P0442 will set.