Patent ID: 8019525

Claim:
A vehicle system, comprising, a battery; an engine including an engine intake, the engine selectively started in response to a battery state of charge falling below a threshold; a fuel tank coupled to a canister through a fuel tank isolation valve; a canister, configured to store fuel vapors, coupled to an engine intake through a canister purge valve, the canister further coupled to a vacuum accumulator through a vacuum accumulator valve; a first pressure sensor coupled to the fuel tank to estimate a fuel tank pressure; a second pressure sensor coupled to the canister to estimate a canister pressure; and a control system with computer readable instructions for, during an engine-off mode of operation, with the fuel tank isolation valve opened and the canister purge valve closed, applying a pressure on the fuel tank first and then the canister, when an absolute value of the fuel tank pressure is above a threshold; applying a pressure on the canister first and then the fuel tank, when the absolute value of the fuel tank pressure is below a threshold; indicating fuel tank isolation valve and/or canister purge valve degradation based on a change in the fuel tank pressure and the canister pressure following pressure application.