“10 Possible Causes When the Check-Engine Light is On”

When the check-engine light is illuminated and stays on the dashboard, it is a sign for you to inspect the engine or take your vehicle to the garage.


Below are 10 common malfunctions that cause the check engine light to turn on, helping you diagnose the problem and prepare financially for repairing your car.

1. Malfunctioning oxygen sensor

A malfunctioning oxygen sensor is the most common cause. It can be due to previous poor repair work or low-quality gasoline, ethanol-blended gasoline that exceeds the standard concentration.

The oxygen sensor provides data for the engine control unit (ECU) to determine the air-fuel mixture ratio from the exhaust gas (EGR system, mentioned in number 9) with air. A faulty sensor can reduce engine power, increase fuel consumption by up to 40%, and increase nitrogen oxide emissions in the exhaust gas.

2. Missing fuel cap

A missing fuel cap is the second most common cause for the check engine light to turn on. Currently, this cause has decreased to 7.21% compared to 9.28% two years ago.

3. Catalytic converter

This is the third most common malfunction. This device looks like a muffler and contains rare metals such as platinum, rhodium, or palladium as catalysts for the combustion of excess gasoline and CO into water vapor and less harmful CO2. A faulty catalytic converter is often due to a weak ignition system that prevents complete fuel combustion.

4. Faulty ignition coil

The ignition coil (or spark coil) provides high voltage to the spark plugs to create an electric spark. A hot engine can weaken or damage the ignition coil.

A faulty ignition coil can prevent the engine from starting. If it is weak, the engine will consume more fuel and may lead to a malfunctioning catalytic converter mentioned above.

5. Spark plugs, ignition wires, and spark plug connectors

Spark plugs, ignition wires, and spark plug connectors can also cause the check engine light to turn on. If you do not fix the ignition system issue, it will consume more fuel and, worse, lead to a malfunctioning catalytic converter.

6. Mass airflow sensor (MAF)

The MAF helps calculate the amount of airflow into the engine and the corresponding fuel injection. If it is faulty, you may have to spend an additional 10 to 25% of fuel.

7. Incorrect installation of alarm devices

If you want to install an alarm device, you should decide before taking the car and have the authorized dealer install the appropriate type. Do not buy and install it yourself because there are many types of alarm devices that may not be compatible with your car’s devices.

8. Evaporative emission control system (EVAP)

When it comes to air pollution caused by cars, people often think of exhaust gases coming out of the tailpipe. Few people know that gasoline vapor escapes from the fuel tank and the fuel line system also causes damage to the environment. Gasoline vapor contains up to 150 chemicals, including highly toxic substances such as toluene, benzene, and sometimes lead.

In older cars, the fuel cap has a small hole for air to enter the tank as the fuel is consumed by the engine. Without this hole, fuel cannot flow into the engine. However, when the engine is turned off, gasoline vapor can escape through this hole and cause air pollution.

To prevent gasoline vapor from escaping into the environment, since 1970, the EPA has required cars to be equipped with an evaporative emission control system (EVAP) to collect and treat gasoline vapor before it evaporates into the atmosphere.

If this system is faulty, the check engine light will also turn on.

9. Replace the exhaust gas recirculation (EGR) system and clean the exhaust pipe

The atmosphere contains 21% oxygen and 78% nitrogen, known as oxygen-rich air. When fuel is mixed with oxygen-rich air and burned at temperatures above 1,500 degrees Celsius, it produces nitrogen oxide (NOx), a harmful gas. To reduce the NOx level in exhaust gas, in accordance with European and American standards, automobile manufacturers must supply the combustion chamber with oxygen-poor air (lower than 21%) by using the EGR device to recover a portion of the exhaust gas (nitrogen, CO2, and water vapor), which is cooled before being mixed with the atmospheric air.

If the EGR system is faulty or the exhaust pipe is clogged, the check engine light will turn on.

10. Faulty battery and charging parts

A faulty battery is often due to its age, overheating of the engine, or hot weather, which also affects the battery life.

Anh Duc (TTTD)