Malfunction sensing apparatus for a fuel vapor control system

A malfunction sensing apparatus for a fuel vapor control system comprising:

• a source of fuel vapor;
• a canister containing an adsorbent for adsorbing fuel vapor and having an inlet and an outlet;
• a check valve connected between the source of fuel vapor and the inlet of the canister and having an operating pressure at which the check valve opens;
• a pressure sensor for sensing a pressure of the source of fuel vapor;
• malfunction sensing means responsive to the pressure sensor for sensing a malfunction when the pressure sensed by the pressure sensor is above a prescribed value;
• and
• prohibiting means for prohibiting malfunction sensing by the malfunction sensing means when the pressure sensed by the pressure sensor is greater than the operating pressure of the check valve.

A malfunction sensing method for a fuel vapor control system, the fuel vapor control system comprising a canister containing an adsorbent and having an inlet connected to a fuel vapor source and an outlet connected to an internal combustion engine, the method comprising:

• isolating the fuel vapor source from the engine so that fuel vapor generated in the fuel vapor source cannot flow to the engine;
• sensing an internal pressure of the fuel vapor source;
• determining a rate of increase of the internal pressure of the fuel vapor source with the fuel vapor source isolated;
• and
• performing malfunction sensing of the fuel vapor control system only if the rate of increase of the internal pressure is below a prescribed value, the malfunction sensing comprising connecting the fuel vapor source to the engine via the canister, sensing the internal pressure of the fuel vapor source, and determining that the fuel vapor control system is malfunctioning if the pressure is above a prescribed level.