A method and apparatus for the testing of vehicle fuel tank caps includes the mounting of a cap to be tested upon a mating socket. The socket/cap combination define a sealed chamber which can be pressurized and/or evacuated in a controlled manner. A pressure transducer monitors the pressure within the chamber. The monitored pressure is compared to reference values to determine cap integrity. The apparatus may be incorporated into a vehicle testing system using microprocessor control and having a database of vehicle, cap and performance data.