Small Leak Test

WARNING: This page is about a different variant/trim than selected.

The engine off natural vacuum diagnostic test is the small-leak detection diagnostic for the Evaporative Emission system. The engine off natural vacuum diagnostic monitors the B150 Fuel Tank Pressure Sensor with the ignition OFF the Q13 Evaporative Emission Canister Vent Solenoid Valve On/Closed and the Q12 Evaporative Emission Purge Solenoid Valve Off/Closed. Because of this, it may be normal for the ECM to remain active for up to 40 min after the ignition is turned OFF.

When the vehicle is running, the temperature rises in the tank due to heat transfer from the exhaust system. After the vehicle is turned off, the temperature in the tank continues to rise for a period of time, then starts to cool and drop. The engine off natural vacuum diagnostic test relies on this temperature change, and the corresponding pressure change in the Evaporative Emission system, to determine if a leak is present.

The engine off natural vacuum diagnostic test is designed to detect leaks as small as 0.51 mm (0.020 in).