Fuel Volatility, Temperature and Vapor Space Compensated Pressure Test for Vehicle Evaporative Systems

The California Bureau of Automotive Repair (BAR) has prepared an inspection/maintenance pressure test for gasoline-powered motor vehicle evaporative systems. The test has been added to the California Smog-Check procedure for 1995 and earlier model-year vehicles. The test pressurizes the vehicle evaporative system to 14″ H2O, followed by a leak decay test. If the pressure decay is more than a specified value, the vehicle is considered to have failed the test. Unlike previous pressure testing performed by the U.S. Environmental Protection Agency and some states, this specified value is fuel volatility, temperature and fill-level dependent. This results in a test which can be expected to consistently pass vehicles with leaks below a certain threshold size, and to consistently fail the majority of vehicles with leaks above this threshold. In initial pre-implementation testing a leak threshold size of diameter 0.0205 inches was used; however, the BAR has not made a final determination of the threshold to be used for implementation.