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  • Writer's picturejianmei huang

5 Common Check Engine Light Codes: What Do They Mean?

The check engine light, that little illuminated icon on your car's dashboard, can be a source of anxiety for many drivers. It seems to appear out of nowhere, often at the most inconvenient times. But what exactly does it mean when that ominous light starts to glow? In this article, we'll explore some of the most common check engine light codes and break them down into simple, understandable terms.

The Ominous Glow of the Check Engine Light

Before we dive into specific check engine light codes, let's understand why this light exists in the first place. Think of it as your car's way of saying, "Houston, we have a problem." When something isn't quite right with your vehicle's engine or emissions system, the onboard computer, known as the Engine Control Module (ECM), detects it and triggers the check engine light.

Now, let's explore some of the most frequent troublemakers when it comes to check engine light codes.

P0016 - Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)

You don't need to be an automotive expert to grasp what this code means. Think of your engine as a symphony orchestra. The crankshaft and camshaft are like the conductor and the lead violinist, coordinating their movements to make beautiful music (or in this case, engine operation). When they fall out of sync, trouble brews. This code signals that their harmony is off-kilter.

If you encounter a P0016 code, it's time to visit your mechanic. Ignoring it could lead to poor engine performance and, ultimately, more significant issues.

P0300 - Random/Multiple Cylinder Misfire Detected

Imagine your car's engine as a well-choreographed dance, with each cylinder playing its part. A misfire occurs when one of these cylinders decides to skip a beat. This code, P0300, tells you that your engine isn't firing on all cylinders as it should.

Driving with a misfire can damage your catalytic converter and decrease fuel efficiency. So, when your check engine light flashes this code, don't delay in seeking professional help.

P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Here's a code that relates to your car's emissions system. Picture your catalytic converter as a magician's hat, responsible for turning harmful exhaust gases into less harmful ones. When the converter's efficiency drops below a certain level, as indicated by code P0420, it means it's not doing its magic effectively.

A faulty catalytic converter can lead to poor fuel economy and increased emissions. So, addressing this issue promptly is not only good for your car but also for the environment.

P0171 - System Too Lean (Bank 1)

Imagine your car's engine as a chef trying to create the perfect air-fuel mixture for combustion. When it gets too much air and too little fuel, it's like adding too much salt to a dish – things don't taste right. Code P0171 tells you that your engine is running too lean, with an imbalance in the air-fuel ratio.

A lean-running engine can result in reduced power, increased emissions, and potential damage to other engine components. It's best to have this issue addressed to keep your car running smoothly.


The check engine light may be a source of anxiety, but it's also a valuable tool for diagnosing potential issues with your vehicle. Understanding the common check engine light codes can empower you to take action promptly and avoid costly repairs down the road. Remember, your car is trying to communicate with you, so don't ignore its messages.


What should I do if my check engine light comes on?

If your check engine light comes on, it's essential to have your vehicle inspected by a qualified mechanic as soon as possible. Ignoring it could lead to more significant issues and increased repair costs.

Can I continue driving if my check engine light is on?

While it's usually safe to continue driving when the check engine light first comes on, it's best to have your vehicle checked at your earliest convenience. Some issues may affect your car's performance and fuel efficiency.

Are there any quick fixes for a check engine light issue?

In some cases, a loose gas cap may trigger the check engine light. Tightening the gas cap may resolve the issue. However, if the light persists, it's advisable to have a professional diagnosis.


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