Leak Detection Pump: Description and Operation

LDP System (Leak Diagnosis Pump)


Vapors containing Hydrocarbons form in the vehicles fuel tank and to prevent them from venting to atmosphere, legislation in the USA demands on-board monitoring of the fuel system sealing on all vehicles powered by an Internal Combustion engine. Beginning with Model Year 2000 these regulations were tightened, and call for detection of a 0.5 mm (0.02 inch) leak.
- The EVAPS system used on the MINI will be the Siemens Leak Detection Pump (LDP). The LDP system is located above the right rear inner fender liner.

The LDP is an electrically/vacuum-actuated device that will pressurize the evaporative emission system for the purpose of detecting leaks and verifying canister purge valve integrity. It has an integrated Canister Vent Valve (CVV) that controls the atmospheric venting of the fuel vapor storage canister.

The LDP assembly is only replaceable as a complete unitized component, however, it is separate from the charcoal canister.

The upper chamber contains an integrated reed switch that produces a switched high/low voltage signal that is monitored by the EMS2000. The switch is opened by the magnetic interruption of the metal rod connected to the diaphragm when in the top dead center position. The repetitive up/down stroke is confirmation to the EMS2000 that the valve is functioning and the basis for determining if a leak is present in the system. The EMS2000 monitors the length of time it takes for the reed switch to open, which is opposed by pressure under the diaphragm in the lower chamber. If this component or its circuits are defective, a fault code will be set and the "Malfunction Indicator Light" will illuminate when the OBD II criteria is achieved.