How to Pass Your Emissions Test

Published April 1, 1999

Sinclair Community College professor James Halderman offers Environment News readers the following tips for passing a vehicle emissions test.

1. Test your vehicle on a nice day only–avoid very cold or windy days. Cold weather requires that the engine be run longer for the coolant, oil, and catalytic converter to reach and maintain optimum operating temperature.

2. Make sure your battery is in good condition. A weak or low-voltage battery causes many fuel-injected engines to run rich (use too much fuel).

3. Change engine oil before having the vehicle tested. Dirty or contaminated oil increases exhaust emissions.

4. Use premium gasoline to help reduce nitrogen oxide (Nox) emissions.

5. Do not overfill the gas tank. After the nozzle clicks off, add no more than a dime’s worth of fuel. If the tank is overfilled, liquid gasoline can be drawn into the engine through the canister purge system.

6. Drive at least 20 miles before having the vehicle tested.

7. Arrive at the test center with only a quarter- to a half-tank of gasoline.

8. While waiting for the inspection, place the gear selector in “park” or “neutral,” and keep the engine running at fast idle (about 2500 rpm).

9. Before testing begins, turn the air conditioning/heating or defroster to the off position.

Other Tips from the Experts

1. Be sure your tires are in good condition and inflated to the maximum pressure stated on the side of the tires.

2. Know whether your car is front- or rear-wheel drive, and watch to see that the test workers put the driving wheels on the rollers.

3. Ask to see that the dynamometer settings are correct for your make, model, and year of vehicle.

4. Watch to see that the parking brake is not engaged.

5. Watch to see that the vehicle operator does not use rapid acceleration or braking. Remember: It is your car, and you are entitled to this information and to observe the test process from a designated safe location. If you suspect your car may have sustained damage, file a complaint and drive to your preferred auto repair facility for an inspection.