Leak Detection

The leak detection is performed by means of 2 main phases:

• Tank system over-pressurizing.
• Leak magnitude measurement.

During leak detection, canister purge valve and canister vent valve (CVV) are closed.

The Engine Control Module (ECU) causes the pump diaphragm to cycle at fixed frequency and for a fixed stroke number. During the pumping, air is drawn from outside into the fuel tank system, and system pressure increases.

Once the tank system over-pressure phase is finished, the leak measurement phase starts. The diaphragm stroke is limited by the top of the diaphragm chamber and a position defined by a reed switch level. The over-pressure slows the diaphragm movement. The pump cycle duration depends on the tank pressure. So the evolution of this time shows the over-pressure level.

If there is a leak, the cycling time or "pulse interval" stabilizes at a rate which compares to the leakage loss.

If there is no leak in the system, the cycling time or "pulse interval" becomes longer.

The "pulse interval" is measured by the ECU, which determines whether or not the leak exceeds a defined threshold. Several "pulse interval" measurements are carried out to secure the test.