DTC P0442: EVAP System - Small Leak Detected: Description

Evaporative Emission (EVAP) system is used to store fuel vapors as to reduce amount of unburned fuel from escaping into the atmosphere. EVAP system consists of EVAP canister, fuel tank pressure sensor, EVAP lines and hoses, EVAP purge solenoid (normally closed), EVAP service port, EVAP vent solenoid (normally open), fuel tank and ECM. ECM monitors EVAP system for circuit faults in fuel tank pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. ECM also monitors EVAP system for large and small leaks. During DTC diagnostic, ECM monitors fuel tank pressure sensor for an atmospheric pressure reading when all DTC parameters have been met with engine running. ECM will then command EVAP vent solenoid on (close valve) and command EVAP purge solenoid to a fixed duty cycle (pulses valve) with engine running. ECM will let pressure drop in fuel tank for a certain length of time after which it will turn off EVAP purge solenoid. If a correct amount of vacuum is achieved, ECM will run DTC P0442 diagnostic, which will monitor decay in vacuum of sealed system over a calibrated amount of time. DTC sets when vacuum decay is more than calibrated amount for a certain length of time due to a small leak.