Leak Detector: Description and Operation

DM-TL (DIAGNOSIS MODULE-TANK LEAKAGE)

OPERATION










The diagnosis module comprises an electromechanically driven (1)-overpressure pump together with a (2)-change-over valve with integrated (3)-reference restriction. In the change-over valve's setting "A" as shown, the pump delivers through the reference restriction. In the other setting the pump delivers through the (4)-canister into the fuel-tank system. The engine-management system measures the pump's electrical current consumption in each setting. A comparison of the current is measured. If the electrical current consumption is identical in both settings, there is a tank-system leak which is equal to the reference restriction. In order to make the procedure independent of environmental influences and tolerances in the overpressure pump, the system performs a comparison with a reference restriction. Outside of the leakage-diagnosis mode, the change-over valve remains in the "A" setting. The canister can be regenerated via a large flow cross-section, and only an insignificant pressure loss occurs. This is advantageous above all on vehicles with high canister-regeneration rates.