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5 Reasons Why Your Car’s Check Engine Light Is On

Your car’s check engine light (CEL) is on. What does that mean?

Don’t panic! A check engine light could be something relating to a loose gas cap, or it could be a sign of something more serious. But before you take your car in for expensive repairs, find out what the problem might be.

We can help you diagnose the problem and get your car back on the road. So, let's take a look at the five common reasons why your CEL may be on.

Loose Gas Cap

Your gas tank's piping and valves are designed for recycling fumes and preventing them from escaping. For example, the check engine light can be triggered by anything as simple as a loose gas cap.

If your gas cap is damaged or you've lost it, you might be wasting gas through evaporation, or your fuel system won't be able to circulate correctly, both of which are CEL-related issues but also rather simple fixes.

Faulty Oxygen Sensor

Check engine lights are often triggered by oxygen sensors. This sensor is in all post-1980 cars' emission control systems. Oxygen sensors guarantee that your engine burns the right quantity of fuel and runs efficiently. It also controls emissions with your catalytic converter.

Over time, oil ash might cover the O2 sensor. This will cause it to stop working properly in its role as a monitor for the ratio of fuel to oxygen in your engine's fuel system, causing the CEL to turn on.

Worn-out Spark Plugs

Worn-out spark plugs can lead to a number of problems for your engine. Over time, the metal in the spark plug will begin to break down and erode.

This can cause an increase in hydrocarbon emissions and a decrease in engine performance. In addition, worn spark plugs can cause an engine to misfire, which can damage other engine components and lead to repairs.

Failing Catalytic Converter

The catalytic converter is an important part of your car's emissions control system. It helps to convert harmful gases into less harmful ones before they are released into the atmosphere.

If your catalytic converter is failing, it can cause an increase in hydrocarbon emissions. This will trigger the CEL to turn on.

Clogged Air Filter

A clogged air filter can cause your engine to run less efficiently. It can also lead to an increase in hydrocarbon emissions.

If you don't replace your air filter when it's supposed to be replaced, it can cause long-term damage to your engine. So, if you see your CEL come on, it is recommended to get your air filter checked and get it replaced as soon as possible.


These were just a few of the common reasons why your check engine light may be on. If you're having trouble diagnosing the problem, we can help. At Euro Car Doctor, we have ASE-certified technicians who can help you to diagnose the issue with your check engine light and will fix it ASAP.

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