What does the service engine light mean on a car?

The service engine light, also known as the check engine light, is an indicator on your car's dashboard that illuminates when the vehicle's onboard computer detects an issue with the engine or other components. This light is designed to alert you to potential problems that require attention, allowing you to address them before they become more serious and costly to repair.

Understanding the Service Engine Light

The service engine light is part of a car's onboard diagnostics system, which continuously monitors various sensors and systems throughout the vehicle. When the computer detects a problem, it triggers the service engine light to turn on, indicating that something needs to be checked or repaired.

The service engine light can illuminate for a variety of reasons, ranging from minor issues like a loose gas cap to more serious problems like a malfunctioning catalytic converter or a problem with the engine's emissions control system. It's important to note that the light does not always indicate a severe problem, but it's crucial to have the issue diagnosed and addressed as soon as possible to prevent further damage to the vehicle.

Diagnosing the Problem

When the service engine light illuminates, the first step is to have the vehicle's onboard computer system scanned for diagnostic trouble codes. This can be done at most auto parts stores or by a professional mechanic, and it will provide valuable information about the specific problem that triggered the light.

• The diagnostic trouble codes will indicate the specific system or component that is malfunctioning, allowing the mechanic to focus their troubleshooting efforts and make a more accurate diagnosis.


• In some cases, the problem may be as simple as a loose or faulty gas cap, which can be easily addressed by tightening or replacing the cap.


• More complex issues may require further diagnosis and repair, such as replacing a faulty sensor or addressing a problem with the engine's emissions control system.

It's important to address the issue as soon as possible, as ignoring the service engine light can lead to more serious and costly problems down the road. Neglecting to address the problem can also result in decreased fuel efficiency, reduced engine performance, and even the risk of further damage to the vehicle.

Preventive Maintenance

To help prevent the service engine light from illuminating, it's important to follow the manufacturer's recommended maintenance schedule for your vehicle. This includes regular oil changes, tune-ups, and inspections of key components like the spark plugs, air filters, and emissions control systems.

• Keeping up with routine maintenance can help identify and address potential issues before they trigger the service engine light, saving you time and money in the long run.


• Additionally, being attentive to any changes in your vehicle's performance, such as decreased fuel efficiency or unusual noises, can help you identify potential problems early and address them before they become more serious.

By understanding the meaning of the service engine light and taking prompt action to address any issues it indicates, you can help ensure the longevity and reliability of your vehicle.

Can I still drive my car if it says service engine soon?

You can likely drive with a solid "service engine soon" light on, but you should schedule a diagnostic check as soon as possible. However, if the light is flashing, it indicates a more serious problem, and you should stop driving immediately to prevent further damage. 
This video explains when it is safe to drive with the service engine soon light on: 57sDespair RepairYouTube · May 16, 2021
Solid light

• Meaning: A solid light usually means a minor issue, such as a loose gas cap or a need for scheduled maintenance. 
• Action: Drive cautiously to a service center for a diagnostic check, but avoid long trips if possible. 

This video explains the meaning of the service engine soon light and what to do: 37sMaxTheCarGuyYouTube · May 1, 2024
Flashing light

• Meaning: A flashing light indicates a serious, immediate problem that could cause significant damage to your vehicle, such as a misfiring engine.
• Action: Pull over as soon as it is safe and have the vehicle towed to a mechanic. Continuing to drive with a flashing light can cause expensive damage to your catalytic converter and other components. 

This video explains what to do when you see a red flashing light on your car: 59sAlley 55 CustomsYouTube · Jan 2, 2021

What is the most common reason for check engine light?

The most common reasons for a check engine light are a loose or faulty gas cap, a failing oxygen sensor, or bad spark plugs. Other frequent causes include a malfunctioning catalytic converter, a dirty mass airflow sensor, or vacuum leaks. 
Common causes
This video explains the top reasons for the check engine light: 47sThe Auto BrainYouTube · May 5, 2025

• Loose or damaged gas cap: A loose or cracked gas cap can allow fuel vapors to escape, triggering the light. This is often one of the easiest fixes. 
• Failing oxygen sensor: The oxygen sensor measures the amount of oxygen in your exhaust. If it's failing, it can lead to a drop in fuel efficiency and turn on the light. 
• Bad spark plugs or ignition coils: Worn-out spark plugs or a failing ignition coil can cause engine misfires, leading to poor performance and triggering the light. 
• Faulty catalytic converter: This component converts harmful exhaust gases into less harmful ones. A failing catalytic converter can cause a significant drop in fuel efficiency and performance. 
• Dirty or faulty mass airflow sensor (MAF): The MAF sensor measures the amount of air entering the engine. Contamination or a malfunction can cause the light to come on. 
• Vacuum leaks: Cracks or leaks in vacuum hoses can disrupt the air-fuel mixture and trigger the light. 

What to do

• First, check that your gas cap is on tightly and is not damaged. 
• If the light remains on, you can use an OBD-II scanner to read the specific code from your car's computer to diagnose the problem more accurately. 
• Some issues, like a loose gas cap or minor vacuum leaks, can be fixed yourself. Others, like a failing catalytic converter or oxygen sensor, may require a professional mechanic. 

What does it mean when your car says service engine?

When your car says "service engine soon," it means the vehicle's computer has detected an issue, which could be anything from a simple need for routine maintenance, like an oil change, to a more significant problem with a sensor or emissions system. It's a good idea to have the vehicle checked to understand the specific cause, as ignoring it could lead to further damage. 
Common causes

• Routine maintenance needed: The light can be a reminder that it's time for a scheduled service, such as an oil change or air filter replacement, based on mileage or time. 
• Loose or faulty gas cap: An improperly sealed gas cap is a very common and simple reason for the light to come on. 
• Faulty sensor: A variety of sensors, like a bad oxygen sensor or a mass airflow sensor, can malfunction and trigger the light. 
• Emissions system problems: This could include a faulty catalytic converter or other issues related to the vehicle's emissions. 
• Minor engine issues: The light can also indicate other minor problems, such as engine misfires, ignition system issues, or low fluid levels. 

What to do

• Check the gas cap: First, ensure your gas cap is on tight and is not damaged. 
• Check fluid levels: Look at your engine oil and other fluid levels to make sure they are not low. 
• Get the codes scanned: Most auto parts stores can scan your car's computer for free and provide you with the specific error codes that triggered the light. 
• Consult the owner's manual: Your manual can provide information specific to your vehicle's maintenance schedule and what the light might mean. 
• Consult a mechanic: A professional can properly diagnose and fix the issue, especially if it's something more serious than a loose gas cap. 

Important note

• If the "service engine soon" light is flashing, it indicates a more serious problem, and you should stop driving the vehicle as soon as it is safe to do so and have it towed to a mechanic. 

What is the most common reason for a service engine soon light?

The most common reason for a service engine soon light is a loose or faulty gas cap, followed closely by faulty oxygen sensors and spark plug issues. These problems often trigger the light by affecting the engine's emissions or fuel-air mixture, and many are related to the car's exhaust system. 
Common causes

• Loose or faulty gas cap: A gas cap that isn't on tight can allow air into the fuel system, interfering with the air-fuel ratio and triggering the light. This is often the easiest and cheapest fix. 
• Faulty oxygen sensor: This sensor monitors the oxygen in the exhaust. If it fails, it can cause poor performance and damage the catalytic converter over time. 
• Worn spark plugs or wires: Worn-out spark plugs and wires can lead to misfires, which will cause the light to come on. You might feel a jolt when you accelerate. 
• Mass airflow sensor (MAF) failure: The MAF sensor measures the amount of air entering the engine to determine how much fuel to inject. A faulty sensor can cause poor gas mileage and other performance issues. 
• Catalytic converter problems: A failing catalytic converter can cause a range of issues, including poor fuel economy, a sulfur smell, and dark exhaust smoke. 
• Low fluid levels: Low oil, coolant, or other fluids can trigger the light, as they are critical for the engine's operation and can lead to overheating or damage. 

What to do

• Check the gas cap first: Make sure it's on tight. If not, tighten it and see if the light turns off after a short drive. 
• Assess your car's performance: If the light is flashing or you notice other issues like loss of power, rough idling, or unusual noises, pull over safely and turn off the engine. This could indicate a serious problem like a major engine misfire that could cause further damage. 
• Use a diagnostic tool: If the light is solid and the car seems to be running fine, use an OBD-II scanner to read the trouble code. This will give you a better idea of the specific problem. 
• See a mechanic: Regardless of the initial check, have the car inspected by a professional to diagnose and fix the root cause.