Patent ID: 7584651

Claim:
A method of diagnosing a fuel tank leak in a fuel tank ventilation system, comprising a fuel tank, an accumulator for fuel vapors and a fuel tank ventilation valve opening out into an intake manifold of an internal combustion engine, wherein the fuel tank, the accumulator and the fuel tank ventilation valve are connected by way of a system of lines and wherein the accumulator has an aeration line with a check valve, the method comprising: immediately before turning off the internal combustion engine, closing the check valve and opening the fuel tank ventilation valve to generate a vacuum in the fuel tank ventilation system; acquiring a vacuum degradation at predetermined points in time when the fuel tank ventilation valve is closed; opening of the check valve in order to bring about a pressure equilibrium with the ambient pressure; again closing of the check valve; acquiring a pressure increase over time at least a predetermined time interval and determining a compensation variable; and determining the presence of a leakage from behavior of the vacuum degradation over time, while taking into account behavior of the compensation variable over time.