Very Small Leak Test

NOTE: "Very small leak test" is only executed for the vehicle other than Mexican specification.

The engine off natural vacuum diagnostic is the very small leak test for the EVAP system. The engine off natural vacuum diagnosis monitors the EVAP system pressure or vacuum after the ignition switch OFF when the monitoring conditions are met.

The engine off natural vacuum diagnosis utilizes the temperature changes and the resulting naturally occurring vacuum or pressure in the fuel tank immediately following a drive cycle. When the vehicle is driven, the temperature in the fuel tank rises. When the vehicle is parked with the engine OFF and ignition switch OFF, the temperature in the fuel tank will continue to rise for a period of time, and then begin to decrease. The engine off natural vacuum diagnosis relies on this temperature change, and the corresponding pressure change to determine if the EVAP system leak is present.

The engine off natural vacuum diagnosis is designed to detect leaks as small as 0.5 mm (0.020 in). The diagnosis can determine if a very small leak is present based on vacuum or pressure readings in the EVAP system.

When a 0.5 mm (0.020 in) leak is present, almost no pressure or vacuum is measured.

If the average of measured pressure from the last 6 measurements is higher than a specified value, "DTC P0456: Evaporative Emission System Leak Detected (Very Small Leak)" sets.