6 Reasons Your Check Engine Light Is On and How to Fix It
Seeing your check engine light come on is something every car owner dreads. This warning light can come on for a number of reasons, ranging from minor problems to serious engine issues. Before you assume the worst, you should become familiar with some of the most common reasons your check engine light comes on. Here are some of the most frequent reasons I’ve seen.
1. Loose or Faulty Gas Cap
A loose or damaged gas cap is one of the simplest causes of a check engine light. Your car’s fuel system relies on a sealed environment to function efficiently. When the gas cap isn’t secured properly, it can trigger an emissions-related warning. This issue can lead to reduced fuel efficiency and even contribute to harmful emissions. This is one of the easiest fixes. You can tighten down the gas cap until you hear it click. If the check engine light still doesn’t turn off, then you might need to replace the cap altogether, which is still a fairly cheap job.
2. Failing Oxygen Sensor
The oxygen sensor monitors the amount of unburned oxygen in your vehicle’s exhaust system. A failing sensor can lead to decreased fuel economy and increased emissions. If ignored, it can damage your catalytic converter, leading to expensive repairs. A common symptom is a noticeable drop in gas mileage. Replacing the oxygen sensor is an affordable fix that can prevent bigger issues.
3. Faulty Spark Plugs or Ignition Coils
Your engine relies on spark plugs and ignition coils to create the necessary combustion for operation. When these components fail, you may experience rough idling, misfiring, or difficulty starting your car. A faulty ignition system can also reduce fuel efficiency and engine performance. Replacing spark plugs is relatively inexpensive and can often be done at home with basic tools. If the problem persists, an ignition coil replacement may be necessary.
4. Malfunctioning Mass Airflow Sensor
The mass airflow (MAF) sensor helps regulate the amount of air entering the engine. If it fails, your vehicle may experience stalling, rough acceleration, or difficulty starting. A dirty or failing sensor can throw off the air-to-fuel ratio, leading to poor performance. Cleaning the sensor with a specialized cleaner can sometimes resolve the issue. However, you may need to replace the MAF sensor if the problem persists.
5. Bad Catalytic Converter
The catalytic converter plays a crucial role in reducing harmful emissions. If it’s failing, your vehicle may produce a rotten egg smell, have reduced acceleration, or overheat. A damaged converter can cause the check engine light to stay on indefinitely. Regular maintenance, including timely oil changes, can help prevent premature failure. Replacing your converter is sometimes needed, but this is a costly repair. So, make sure it’s what will actually help before moving forward with this job.
6. Issues with the EVAP System
The evaporative emission control (EVAP) system prevents fuel vapors from escaping into the atmosphere. A leak, damaged hose, or faulty purge valve can trigger the check engine light. Symptoms may include a fuel smell, difficulty starting the car, or reduced performance. A mechanic can run a smoke test to identify leaks in the system. Once the faulty component is found, replacing it should clear the issue.
Don’t Ignore the Warning
It’s never a good idea to ignore your check engine light. Shrugging it off could lead to more severe and expensive issues with your vehicle. Many auto parts stores will provide you with a free diagnostic scan that can tell you if it’s something small like a new gas cap needed or something you need to take to the shop to get fixed. As always, performing regular maintenance on your car will help you avoid some of these issues. So, take care of your vehicle and do what you can to address problems promptly.
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Drew Blankenship is a former Porsche technician who writes and develops content full-time. He lives in North Carolina, where he enjoys spending time with his wife and two children. While Drew no longer gets his hands dirty modifying Porsches, he still loves motorsport and avidly watches Formula 1.