Small Leak Test

The engine off natural vacuum (EONV) diagnostic is the small leak diagnostic for the evaporative emission (EVAP) system. The EONV utilizes the dynamic temperature changes in the fuel tank immediately following a drive cycle to generate natural vacuum or pressure in the fuel tank. While previous leak detection was performed with the engine running, the EONV monitors the EVAP system with the key OFF. The control module will remain active for up to 45 minutes after the engine is turned OFF. The EONV test monitors the fuel tank pressure (FTP) or vacuum as the fuel changes temperature to determine if a leak is present. If the system is truly sealed, there will be a pressure and/or vacuum change as the temperature of the fuel changes. Pressure or vacuum changes that are less than the calibrated values indicate a leak. The EONV diagnostic is designed to detect leaks as small as 0.51 mm (0.2 inches). The procedure for locating and repairing the EVAP system leaks is the same for the EONV as with the other EVAP systems. If the test reports a falling value, DTC P0442 will set.