Vehicles with front-wheel drive should have the front suspension properly aligned. Poor front-end alignment will make the vehicle difficult to test on the dynamometer. A gas cap is a required piece of equipment. It must be the correct type for your vehicle and actually be in place. Make certain your brakes are in good condition.
Poor brakes make the vehicle difficult to test on the dynamometer.
Ensure the integrity of your exhaust system. Excessive exhaust leaks may cause your vehicle to be rejected from the emissions and may be dangerous to the vehicle's occupants. The emissions control equipment for your vehicle must be intact and functioning. Vehicles missing a catalytic converter will be rejected from the emissions test if that model vehicle was originally equipped with a catalytic converter. Removing or tampering with emissions equipment may cause your vehicle to fail the test.