Top Five Reasons Why a Car Fails An Emissions Test


You have to get an emissions test every two years in Illinois unless your automobile meets the exemption requirements. If your car fails the test, you won’t be able to register it until you get it fixed and it passes the second smog check. Clark’s Car Care is an emissions testing station in Naperville, IL. We can test your car, truck, or C/SUV and diagnose the reason why it failed if it fails. We can also fix it.

1. Bad Oxygen (O2) Sensor

The oxygen sensor can be double trouble. If it’s failing, it will not only turn on your check engine light, but it will also cause your automobile to fail an emissions test. The O2 sensor monitors exhaust to ensure the correct amount of oxygen is released in it. A failing sensor will return an emissions failure and could also cause engine performance problems and overheating.

2. Failing Catalytic Converter

The catalytic converter has a huge responsibility: It takes carbon monoxide and converts it into carbon dioxide before the gas is exhausted out of your tailpipe. Much like the O2 sensor, you will get a check engine light warning and fail the emissions test if the catalytic converter is going bad. This is because there’s too much carbon monoxide in your exhaust.

3. Faulty EVAP System

EVAP stands for Evaporative Emission Control System and unless you drive a classic car, your vehicle has an EVAP system. This system’s sole purpose is to prevent gasoline vapors from entering the atmosphere unless under controlled conditions. If your vehicle has a vacuum hose or vent leak, or if the gas cap is too loose or has a broken seal, your vehicle will fail an emissions test.

4. Fuel Metering/Mixture Problems

Your vehicle has a combustion engine and it uses air and fuel to help create this combustion. It has two parts to help meter the air/fuel mixture sprayed into the combustion chamber: the mass airflow sensor and the fuel injection unit. If either fails, you could end up with a rich fuel mixture – a mixture too heavy in fuel – and your automobile will fail the emissions test.

5. Worn Spark Plugs

The spark plugs generate the spark that ignites the air/fuel mixture sprayed into the combustion chamber by the fuel injectors. If the plugs are worn, misfiring, or set in the wrong firing sequence, your vehicle could fail a smog check. Check your owner’s manual to see when you should change your spark plugs and do so if they’re due or overdue for replacement.

Clark’s Car Care in Naperville, IL, is your one-stop-shop for emissions testing, diagnosis, and repairs. Set up an appointment today.

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