All About Emissions: Passing the Test


Most of us have a basic understanding of why a car needs an emissions test.  The EPA tells us that 75% of carbon monoxide pollution in America is from motor vehicles. So in order to reduce this number, we have to periodically test our vehicles for emissions to make sure we are not completely destroying the environment.

You may ask, “Why do I need an emissions test if my car is still new?” We often think that the only culprits that cause carbon monoxide pollution are the clunkers we see driving down the road, held together by duct tape and bungee cords.


While they are quiet the eye-sore, they are just as guilty as newer cars that may only be 4 years old when it comes to emissions. Under each hood, there are common problems that occur in every vehicle to make you fail an emissions test.

High Hydrocarbons

There are different types of gas analyzers used in emissions tests to measure the levels of emission gases in a vehicle. Specifically the gases being tested for are CO2, nitrogen, and hydrocarbon.  Hydrocarbon is raw gasoline. The more gasoline your vehicle’s engine combusts completely, the less pollutants are emitted into our air. Having high hydrocarbon in your car are caused by something as simple as having bad spark plugs or improper air/fuel intake. Make sure you are regularly replacing air, oil, and fuel filters, as well has replacing your spark plugs when needed.  If you stay up-to-date on your vehicles scheduled maintenance, then this will greatly reduce the probability of having high hydrocarbons.


The DLC Scanner or Diagnostic Link Connector Scanner is used to scan the electrical components in your car to make sure the ECU is working properly. The Engine Control Unit (ECU) is the brain behind all the inner-workings of your vehicle. The ECM also makes sure the car meets emissions standards, by monitoring and regulating the fuel mixture to ensure the engine isn’t running too rich and emitting pollutants beyond the established parameters. If the ECU isn’t working properly, then the sensors that monitor fuel mixture may not light up on your dashboard. It’s good to take your car to an auto shop for a diagnosis before you take an emissions test. The auto shop should tell you whether or not you have an ECU problem and if all sensors are working appropriately.

Note: If your check engine light is already on, you will automatically fail your emissions test. Get your car into a shop to fix the issue so that you don’t have to pay more money to retake the emissions test.

Failing your emissions

Make sure you don’t put off your emissions test too close to your registration renewal date. If you fail your emissions test then you can’t renew your registration, meaning you can’t legally drive your car until you pass the test. If you find yourself having to go to an auto shop because of a failed emissions test, hold on to all the paperwork that you received from the testing center and the auto shop. This will help you qualify for a waiver to pass the emissions test if you failed the retest. You can read more about the waiver requirements on the Illinois Vehicle Emissions Test Program.

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If you need to have your vehicle checked for emissions, feel free to give us a call. specializes in European auto repairs and maintenance. We strive to keep our service cost 40% less than dealerships. Schedule an appointment for your Audi, BMW, Land Rover, Mercedes, Mini Cooper, or Volkswagen with us

Written by Spotlight Automotive