US Patent 7124018 Method for diagnosing a tank venting valve

A method for testing the operability of a tank venting valve between an internal combustion engine and a fuel vapor storage device of a motor vehicle. The stored fuel vapor from the fuel vapor storage device is fed to the internal combustion engine when the tank venting valve is open and a reaction from a fuel/air control loop is analyzed to diagnose the operability of the tank venting valve. In order to refine the method so that a diagnosis that is as far as possible not subject to error may be performed when not idling, the stored fuel vapor from the fuel vapor storage device is fed to the internal combustion engine at least twice in one driving cycle while the tank venting valve is open, a reaction of the fuel/air ratio control loop being detected each time and the operability of the tank venting valve being inferred by comparing the detected reactions.