Maintenance Useful tips

6 common causes of the engine warning light turning on


When the engine warning light turns on, it indicates that trouble has occurred inside the engine.
Various problems could cause this, but at this time I will introduce six common causes.


There are a lot of reasons for the engine warning light to illuminate.
The most common cause is due to abnormalities being detected by sensors attached to the engine and its surroundings, or breakdown of the sensor itself.

O2 sensor

The O2 sensor is a sensor that measures the concentration of oxygen (O2) contained in the exhaust gas and reads the combustion state of the engine.

If there is an abnormality in this O2 sensor, fuel consumption can become worse, and the catalyst attached to the muffler that removes harmful substances can become clogged with soot.

Although the engine will not stop or break down immediately, if you leave it in this state, the worst case scenario is that the catalyst becomes abnormally hot and there is a danger of igniting nearby flammable objects.

The life of the O2 sensor is said to be roughly 10 years or 100,000 km in domestic cars.
If the engine warning light turns on when the car is close to either of these numbers you should have the O2 sensor checked.

Ignition sensor

The ignition sensor plays the role of keeping the ignition timing of the engine optimal.
If the ignition timing is shifted for some reason, the engine warning light will show.

Because incomplete combustion is occurring, it is okay to drive a little, but fuel efficiency will get worse, the car will become powerless, and eventually the engine may break down.

A symptom of this may be the engine shaking and vibrating differently than usual.
One thing that is common is that one of the spark plugs will not ignite and the engine will move with one less cylinder, which causes this abnormal vibration.

Airflow sensor

The airflow sensor is a sensor that measures the amount of air being sent to the engine, and is responsible for feeding the optimum mixture (fuel mixed with air) to the engine.

If the air cleaner has not been maintained for a long time, clogging will occur. The amount of air will decrease and the engine warning light will light up.

Since the airflow sensor itself does not cause abnormality or failure itself, you should check the parts of the intake system including the air cleaner when the warning light turns on.

Crank Angle Sensor and Cam Angle Sensor

The crank angle sensor keeps track of the angle of the crankshaft that changes the vertical motion of the engine to rotational motion.
The cam angle sensor monitors the angle of the camshaft, which rotates, moving the valves and opening and closing the intake and exhaust inlets.

If this sensor signals an abnormality, the engine loses the optimal ignition timing, so combustion efficiency drops and fuel efficiency gets worse. The car will lose power, and in some cases, the engine may stop running.

Accelerator opening sensor

The accelerator opening sensor is a sensor that measures how much the accelerator is depressed.

The main function of this sensor is to measure how much air enters the fuel injector and communicate it to the electronic control unit.

Therefore, if an abnormality occurs in the accelerator opening sensor, not only fuel consumption and output will be affected, but also many electronic control devices related to the running of the vehicle will be faulty. This may cause trouble when driving.

Battery sensor

The battery sensor is responsible for monitoring degradation of the battery and efficient operation of the alternator.

One reason the battery sensor detects an abnormality is that often the battery was replaced incorrectly, by connecting the battery cable and the terminal improperly.

If you are replacing the battery yourself or unplugging the battery cable from the battery terminal for some work, you should check the connection status again.

Since the battery sensor is directly connected to the electronic control unit, short-circuiting the battery may cause failure of the battery sensor as well as of the electronic control unit.
If you are unfamiliar with car batteries, you should leave it to a professional.

As mentioned above, six reasons for the engine warning light showing up have been introduced.
However, there are many other causes for this to happen.

If the engine warning light turns on, you should ask a mechanic to take a look.

-Maintenance, Useful tips

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