29 August 2025
9 Common Reasons Your Check Engine Light Is On
Most car owners make sure to complete the basic tasks necessary to keep their cars in good condition, such as maintaining the ideal tire pressure, topping up their windshield fluid, and scheduling regular services. While practices can help, most people often tend to overlook the smaller details that can lead to bigger problems. The check engine light (CEL) is one such warning sign that can be easily overlooked. Commonly observed as orange, yellow, or amber in color and in the shape of a small-car engine, the check engine light can indicate varying issues, ranging from minor problems such as a damaged gas cap, weak battery, or malfunctioning oxygen sensors to serious issues like a defective catalytic converter, transmission problems, or critical sensor failures.
An important detail to notice is whether your check engine light is steady or blinking. A steady light indicates that there are minor problems that should be taken care of in the near future, whereas a blinking light indicates more serious problems. Be it minor or major, identifying the real reason why your check engine has turned on should remain in focus. In this blog, we’ll explore the basics of how the check engine light functions and the common reasons why it turns on.
Common Reasons for Check Engine Light
For most of history, Indian cars had a very basic dashboard, comprising a few warning lamps that indicated oil pressure, battery charge, and similar issues. These signs were helpful but limited, as they only alerted drivers after the issue had occurred. Gradually, as emission norms became stricter in the country, car manufacturers introduced the On-Board Diagnostics (OBD) systems. These systems were instrumental, as they completely changed the way cars showed signs of malfunctions or issues. The in-built computer system would track the vehicle’s performance and would warn the drivers of potential problems. One of the main features of the OBD system was the check engine light, a warning lamp that would indicate whenever the system picked up unusual signs. Although the check engine light warning could be frightening, in most cases, there are minor and easy-to-fix problems that cause it. Here are a few of the most common reasons why the check engine light will come on in your car and how to go about fixing the problem:
Loose or Faulty Gas Cap
A car's gas cap maintains the pressure of the fuel system and prevents the fuel vapors from escaping. Oftentimes, your car sensors may pick up something as simple as a loose or broken gas cap as an issue and turn on the check engine light. It occurs when the sensors of a car note the increased evaporative emissions and sound it as a complication. Such a problem can be easily eliminated by tightening the gas cap until you hear the clicks or replacing the gas cap in case it is already broken.
Faulty Oxygen Sensor
The oxygen sensor in a car measures the level of unburned oxygen in the exhaust system. When it malfunctions, it can send inaccurate readings, leading to problems like reduced fuel efficiency, rough engine performance, and higher emissions.In the long run, this can damage your car’s catalytic converter. It is important to have a professional take a look at your car so as to replace the faulty sensor.
Bad Catalytic Converter
The catalytic converter minimizes harmful exhaust gases by transforming them into less toxic emissions.A malfunctioning catalytic converter can cause your vehicle to emit higher levels of emissions and run less efficiently. It is often a lack of proper maintenance that causes the catalytic converter to fail.Depending on the extent of the damage, your catalytic converter may need to be repaired or replaced.
Faulty Mass Airflow Sensor (MAF Sensor)
The MAF sensor accurately measures the air entering the engine, allowing the computer to calculate the correct fuel-to-air ratio. If it malfunctions, it can lead to problems like stalling or difficulty starting the engine. You just need to clean the filters to fix these issues. However, some situations call for a complete replacement.
Worn-out Spark Plugs or Ignition Coils
Spark plugs and ignition coils together ignite the fuel-air mixture in the combustion chamber to turn on your car and keep the engine running. Worn-out spark plugs or ignition coils may also result in your car misfiring and causing impaired performance and low fuel consumption. This problem can be eliminated through regular maintenance
Vacuum Leak
Your car’s engine depends on a vacuum system to control all the major engine functions, such as fuel delivery and emissions. Cracked hoses or loose gaskets can cause a vacuum leak, which can lead to stalling and spikes in RPMs for the car. A professional mechanic can help identify such issues and fix them through proper replacement.
Faulty Exhaust Gas Recirculation Valve
The EGR valve helps reduce nitrogen oxide emissions by recirculating most of the exhaust gases back into the combustion chamber. If any valve of this system gets clogged or damaged, it can lead the car to experience performance issues. Regular cleaning of this valve can help to solve the issues.
Failing Battery
The car’s battery supplies power to all electrical components, including the starter motor and ignition system. A weak or failing battery, along with unstable voltage levels, can create irregular signals that may trigger the check engine light. Dimming lights and electrical glitches are also signs of this issue. This issue can only be sorted by replacing the battery with a fresh one. The above are some of the common causes that flip on the check engine light. However, it is important to check in with your local mechanic or service center for an accurate diagnosis.
Also read, How to Prevent Common Causes of Battery Drain?
Staying Alert to Your Check Engine Light
If your check engine light turns on, it doesn’t necessarily indicate major issues. However, having an understanding of what causes this can help you diagnose this issue, alone or with professional help, before it grows more serious. Do not ignore the CEL, as it can damage your car's engine in the long run. It is important to note that regular maintenance and repairs can help eliminate unexpected problems and keep your CEL off!
At Indus Used Cars, every vehicle undergoes a thorough multi-point inspection by certified technicians. From checking the engine and transmission to testing the battery, brakes, and emission systems, we ensure that potential issues are fixed before the car reaches you. Regular servicing, genuine spare parts, and quality checks help us guarantee that each car is reliable, safe, and ready for the road.