Emissions Testing 101: 3 Reasons Your Vehicle Might Fail Emissions Testing

Preserving air quality is something that is becoming increasingly more important in today's modern world. Vehicle pollution can contribute significantly to air pollution levels, so most municipal governments require vehicles to pass an emissions test before deeming them safe to operate on public roadways.

Failing an emissions test can be stressful, but understanding why your vehicle might not pass can be vital in addressing problems. Familiarize yourself with these three common reasons a car might not pass emissions testing.

1. An oxygen sensor that isn't working.

Your vehicle is equipped with oxygen sensors that are designed to measure oxygen levels in your vehicle's emissions. When these sensors begin to malfunction, the amount of pollution being released by your vehicle can increase.

Faulty oxygen sensors are also associated with overheating and sluggish acceleration. Watching for these signs can help you better determine if your vehicle's oxygen sensors will pass future emissions testing.

2. A failing evaporative emission control system.

The gasoline that fuels your car can quickly turn into a vapor when exposed to the high operating temperatures within your vehicle's fuel system. This vapor needs to be contained in order to prevent it from being released into the atmosphere, and it is contained by your vehicle's evaporative emission control system (or EVAP).

Should any component within the EVAP begin to malfunction, your vehicle will likely fail an emissions test. Common causes of a failing EVAP include a loose gas cap, leaks in the hoses that service your fuel system, and faulty valves. An experienced mechanic at your local auto repair shop will be able to source the problem so that you can fix it as quickly and cheaply as possible.

3. Spark plugs that are worn.

Your vehicle's spark plugs play a critical role in the ignition process. When these spark plugs begin to wear out, they could cause your vehicle to fail an emissions test. During emissions testing, a technician will check your vehicle's ignition system for the presence of high hydrocarbons.

Worn spark plugs can fail to fully ignite all of the fuel within your vehicle ignition system, leaving high hydrocarbons behind. Replacing the worn spark plugs with new ones should eliminate high hydrocarbons, allowing your vehicle to successfully pass an emissions test in the future.

Being prepared to address some of the problems that might cause your vehicle to fail an emissions test will allow you to keep your car in better running condition.