Device and method for testing the seal tightness of a fuel tank system of a motor vehicle

A method for testing seal tightness of a fuel tank system of a motor vehicle, wherein excess pressure is built up in the fuel tank system by an electrically operated pump and electric current consumption of the pump is compared to reference values to determine whether the seal tightness of the fuel tank system is sufficient, and wherein the fuel tank system comprises a filler neck with a locking fuel tank cap, the method comprising the act of:

• determining a switch state of an electric tank cap switch, based upon an electric current;
• wherein the electric tank cap switch has a different switch state when the filler neck is closed properly than when the filler neck is not closed properly;
• wherein a control line connected in parallel to a power supply line of the pump is guided across the electric tank cap switch;
• and
• wherein, in at least one of the control line and the power supply line, an electric resistor is installed, and in the control and power supply lines the electric current develops when the filler neck is not closed properly during operation of the pump.

A method for testing seal tightness of a fuel tank system of a motor vehicle, comprising the acts of:

• determining the seal tightness of the fuel tank system, based upon an amount of current;
• wherein the amount of current depends upon a switch state of an electronic tank cap switch;
• and
• wherein the tank cap switch is closed when a filler neck of the fuel tank system is not closed properly and a resistance element is provided in a control line of the tank cap switch.

A method for testing seal tightness of a fuel tank system of a motor vehicle, comprising the acts of:

• determining the seal tightness of the fuel tank system, based upon an amount of current;
• wherein the amount of current depends upon a switch state of an electronic tank cap switch;
• and
• wherein the tank cap switch is closed when the filler neck is closed properly and a resistance element is provided in parallel with the tank cap switch.