Patent ID: 7578286

Claim:
A method for the functional diagnosis of an activateable fuel tank ventilation valve of a fuel tank system of an internal combustion engine, especially of a motor vehicle, the method comprising: adding regeneration gas to air drawn into a combustion chamber in specifiable time intervals when the fuel tank ventilation valve has been activated to open; delivering fuel to the combustion chamber; combusting the fuel, the air, and the regeneration gas in the combustion chamber; comparing at least a first parameter, which characterizes combustion of fuel and intake air, with a second parameter, which characterizes combustion of fuel, intake air and regeneration gas; calculating the regeneration gas stream from the changes between the first parameter and the second parameter, wherein the HC-concentration of the regeneration gas is specifically affected by changing the regeneration gas stream; comparing the calculated regeneration gas stream with a pre-determined characteristic curve of a fuel tank ventilation function; inferring the fuel tank ventilation valve being functionally efficient if the calculated regeneration gas stream is within a range of tolerance specified in the characteristic curve; and inferring the fuel tank ventilation valve being functionally inefficient if the calculated regeneration gas stream is not within a range of tolerance specified in the characteristic curve.