How can I prepare for an emissions inspection? Why is my vehicle being tested? Your vehicle’s engine, just like millions of other vehicle engines all over the world, can be a significant producer of three pollutants considered to be hazardous to your health: ▪ Hydrocarbons (HC), which occur when your vehicle's combustion process isn't complete. ▪ Carbon Monoxide (CO), which develops when your vehicle's air/fuel mixture doesn't have enough air. ▪ Oxides of Nitrogen (NOx), which reacts with sunlight to form smog. Your vehicle is tested to ensure that it's continuing to run as clean as it was designed to, and if it isn't, to identify which pollutants are being produced in excessive amounts, and need to be brought under control by having your engine serviced. Are my vehicle's emissions really a serious problem? Consider the facts: Motor vehicles are the single largest cause of carbon monoxide air pollution and ground-level ozone (smog) on this planet. In a typical city, cars and trucks cause up to 75% of the hydrocarbon emissions that cause smog and 90% of all carbon monoxide pollution. 30% of all vehicles that are 5 to 7 years old put out excessive emissions. 55% of all vehicles 7 or more years old exceed emission standards. Your vehicle's emissions do make a difference, and it's a difference that will ultimately benefit you. How does my vehicle control emissions? Modern vehicles control emissions two ways. First, they're designed to burn gas more efficiently than ever before. This automatically reduces the amount of pollution the engine produces, since pollution is typically caused by inefficient combustion. Second, today's vehicles have special devices within them that are designed to reduce emissions output even further. When your engine is running, sensors in and around the engine continually detect and analyze an extraordinary range of information – from engine load to the amount of oxygen in your exhaust, and much more. The information these sensors transmit to your on-board computer tells the computer how to set and control performance components that include your vehicle's fuel injectors or fuel pump relay, idle air and speed controls, catalytic converter and dozens more. These "sense-analyze-control" processes happen many times each second. Even a minor malfunction in a single component can ultimately increase your emissions significantly. Why does a vehicle fail emissions testing? Generally, there are two reasons why a vehicle won't pass an emissions test. A critical emissions control component, such as the catalytic converter or oxygen sensor may have malfunctioned or failed. This alone may be enough to raise emissions to unacceptable levels. More common however, a vehicle fails emissions testing simply because it hasn't been properly maintained. The on-board computer's job is to keep the engine running as efficiently as possible for as long as possible. When the sensors detect a component or system that's wearing out or malfunctioning, the computer compensates for the problem by telling other related components to operate differently. If this process of compensation has been going on long enough, the vehicle seems to be running fine but actually all the proper control settings have been altered enough to allow excessive emissions to occur. Back to Things You Should Know Visit our Resource Library for available downloads