Don't overfill your gas tank. When filling your tank, resist the impulse to get just a little bit more into the tank after the nozzle clicks off. This excess gasoline has nowhere to expand so it saturates a part of the emissions control system resulting in increased emissions.

Make sure your brakes are in good condition. Poor brakes can make the vehicle difficult to test on the dynamometer, and may cause the vehicle to be rejected from testing.

Make sure your tires are properly inflated. Tires that are unevenly inflated, under-inflated or mismatched make the vehicle difficult to test on the dynamometer, and may cause the vehicle to be rejected from testing.

Ensure the integrity of your exhaust system. Excessive exhaust leaks can cause your vehicle to be rejected from testing. Exhaust leaks are also dangerous to the vehicle's occupants.

Fully warm up your vehicle before testing. Until your vehicle is at normal operating temperature, it emits excess pollution. Run your vehicle at highway speed for at least 15 minutes prior to undergoing an emissions test. Limit use of air conditioning and defroster if possible.

Check to see you have a gas cap in place. This is required equipment. It must be the correct type for your vehicle, and it must have a tight seal. A missing or leaky gas cap will cause your vehicle to fail the test.

Your vehicle's emissions control equipment must be intact and functioning. Missing or tampered emissions control equipment will cause your vehicle to fail the test.

Make sure your vehicle does not smoke. Visible smoke is a sure sign of excess pollution and will cause your vehicle to fail the test.

Follow recommended maintenance schedules for your vehicle. Read your owner's manual, and follow maintenance guidelines. Your vehicle will perform more efficiently.

Front-wheel drive vehicles: Make sure the front suspension is properly aligned. Poor front-end alignment will make the vehicle difficult to test on the dynamometer, and may cause the vehicle to be rejected from testing.