Check Engine Light - 10 most common causes

Check Engine Light

Almost every modern car has an indication light named “Check engine” on the dashboard, which might be strange for some people when it lights up for the first time and when it does, you may have to deal with loads of unpleasant problems. That being said, some people can ride their car all their life with this indication on, thinking why is my check engine light on and not going any further.

So what does check engine light mean and what are the unpleasant sides for today’s car owners? I will try to give answers to these and many other questions.

First of all, if you never faced this indication, you are very lucky person (and in case you don't even know where it is, check engine light is located on your car’s dashboard). In the case of flashing check engine light, machine wants to inform you that the control unit has found some fault in the engine. Initially, "Check Engine" role was done by mini-computers and their main task was to manage the catalytic converter, but over time the duties and the field of coverage for this indicator has increased significantly.

Car Dashboard

Modern instrument control panels' check engine indicator is related to composition of the fuel mixture, engine speed, ignition and many other parameters. As a result, there are many possible reasons for it to light up and when it does, without specific knowledge or skills it is very hard to understand what the problem is and in some cases even having special tools won’t directly help you to understand the root cause of the problem, not even talking about resolving it.

First of all, you must understand when it is normal for engine check indicator to light up, and when it is indicative of the engine malfunction.

* If the indicator lights up when you start the engine and then goes off, there is no need for any concerns, the engine is working OK. If the check engine indicator comes on when you start the engine and does not go out for a long time, it is likely to have a fault in the engine, but do not panic, because it may quite be not a serious issue. That being said, never underestimate or neglect this indication, you may not know what the issue is on first sight, but this can be critical for your engine.

* In case of check engine light flashing when the vehicle is in motion, the reason may be the low level of oil. Stop the car and listen to the engine, if it had any extraneous noise or knocking, make a visual inspection for damage to the hull and smudges. If you find any issues, eliminate them on arrival home, however if the visual inspection failed to find anything, you should visit the service station and get help from professionals armed with special equipment in order to quickly and accurately establish the root cause of check engine indicator light up. Just a side note, if the engine works despite check engine indicator being on, maybe the problem lies in the spark plug, one of them may be misfiring.

Car Repair

As I mentioned, because signal comes directly from the board computer whose task is to monitor a large number of systems (the carburettor, ignition, automatic transmission, the engine as a whole and a lot more) there are quite a lot of reasons for which the check engine can light up. Regardless of the complexity of check engine signal, in some cases, you can try to diagnose and identify faults yourself. In order to help you with it, I have given below a list of 10 possible causes for which check engine indicator can light up, along with possible solutions.

1) Low Quality Fuel

Low-quality fuel can be the cause of check engine indicator to light up. The solution is to drain the "bad" fuel and fill the tank with high quality one. If you neglect draining the non-spec oil and insist on driving with the fuel already in, most probably you will have to service engine soon. After high quality fuel is in the engine, this will reset check engine light.

2) Loose Gasoline Cap

It may sound nonsense to you, however if gasoline cap is loose or there is a crack on the gasoline cap, it will cause the check engine light to go on. Therefore, as an initial check when “Check engine” indicator lights up, please check gasoline cap, which ideally should sit tight. If it doesn't, or there is crack on the cap, consider replacing, it isn't a very expensive item.

3) Failure of High Voltage Wires

Another most common reason why check engine light pops up is fault of high voltage wires. Therefore, when check engine light flashing, it is advisable to service engine soon and do thorough inspection of high voltage wires. If any faulty high voltage wire found during inspections, think about direct replacement, as repaired wires most probably will create same issue down the road and check engine light issues will be visiting you on and .

4) Faulty Spark Plugs

Faulty spark plugs, improper gap in spark plugs or cracked insulator can cause the check engine light to come up. So you should go and check engine to find out what is going on with spark plugs. Directly replace spark plug, if faulty one identified, without even trying to repair it. Be aware that the gap between the electrodes must not exceed 1.3 mm which will create problems, especially during cold start. If you have loss of power, difficulty to start or engine hesitation, then you should service engine soon and checking spark plugs.

5) Under-performing ignition coil

There can be problem with ignition coil, which (generally speaking) transforms low battery voltage to high voltage in order to enable spark plug to create a spark. So if there is problem with providing spark for ignition, check engine light will go on. In this situation, check whether there is a spark and then check the resistance across the terminals of the coil. While checking primary resistance, ohmmeter should show value between 0.75 to 0.81 Ohms and for secondary resistance is should be 10,000 to 11,000 Ohms.

6) Fault of Oxygen Sensor

Oxygen sensor (aka Lambda probe) often causes check engine light to light up. Oxygen sensor plays critical role of monitoring amount of oxygen going to the engine for right fuel-air concentration. So if there is problem with oxygen sensor, engine won’t clearly understand how much oxygen is required for proper combustion and due to excess or less oxygen, engine will start working improperly. As a consequence, you will see check engine light flashing. To identify condition of oxygen sensor, you have to check it with multimeter and in the case of failure, you need replacement rather than trying to repair.

7) Malfunction of Catalyst Converter

Catalyst converter is located on the engine exhaust and provides transformation of engine exhausts through chemical reactions from hazardous substances into non-hazardous ones. Mainly three chemical reactions going there are:

* Converting carbon monoxide into carbon dioxide: CO + 1/2O2 -> CO2

* Converting non-burnt hydrocarbons into water and carbon dioxide: C3H6 + 9/2O2 -> 3CO2 + 3H2O

* Converting nitrogen oxides into carbon dioxide and nitrogen which exists in the air: NO + CO -> N2 + CO2

If there is problem with catalyst converter check engine light will light up. This time check engine light flashing is mainly due to overheating, contamination and clogging of catalyst converter.

* When temperature of catalyst converter rises to certain high temperature check engine light will light up. The reason mainly will be failure of oxygen sensor to let engine understand required amount of fuel and air. As a result, rich amount of fuel and air will cause catalyst converter temperature to go high.

* Contamination and finally clogging of catalyst converter can be due to coolant leaking to the engine, oil burning by engine and/or excessive non-burnt particles going to the catalyst converter, which in return will cause contamination or clogging of the catalyst converter. In order to minimize or eliminate chance of these, it is required to regularly monitor emissions of your car. Monitoring is important, as unplanned repair of catalyst converter will cost a lot and it is not an easy repair. The only solution is to replace it as catalyst converter is single-use item. Generally, catalyst converter needs replacement after each 150,000 kilometres or 100,000 miles.

8) Dirty Fuel Injectors

Clean fuel injectors and correct spray pattern are ensuring high performance of your engine. However, when fuel deposits build up on the injector, they will start clogging. As a result, performance reduces, which consequently causes hesitation, lean misfire, loss of power, high fuel consumption and as a result, turns check engine light on. If you ask where these deposits are coming from, by the time engine is off, left-over fuel’s light portion evaporates and waxy residues are left on it, as there is no flow of fuel through fuel injector when engine is off. So in order to get rid of check engine light lighting up, it is required to clean the fuel injectors and if any fuel injector is beyond cleaning limits, replace them to let check engine light to go off.

9) Problem with Fuel Pump and Filter

Fuel pump and filter are not monitored directly, however if there is a problem with the fuel pump and fuel filter, it will cause less fuel going to the engine. When insufficient fuel goes to the engine, it will cause loss of power, misfire, etc. of the engine, which eventually will result in check engine light flashing. In order to remove check engine indication, you need to do some pre-check before deciding any replacement. Firstly, rail pressure (the pressure of the fuel applied by injector) should be checked and it should be made sure that pressure is not less than 3 bars. If fuel injection pressure is right, the problem could be due to clogging of fuel pump filter or fuel pump itself might be faulty. Therefore try to clean the filter or mesh in the tank and if it is necessary, completely replace the fuel pump.

10) Failure of Mass Air Flow Sensor

Mass Air flow sensor (generally speaking) monitors and counts amount of air flowing to the engine. Measuring amount of air is very important in order to have correct oxygen and fuel mixture during burning process. So if there is any problem with mass air flow sensor, your engine won’t understand amount of air flowing to the engine and will start working abnormally by showing sign of misfire, excess fuel consumption, engine hesitation both during start-up and normal operation. In order to remove check engine light, you would need to clean mass air flow sensor, however it is not easy thing to do. You should be very careful to avoid delicate wires of sensor, while trying to clean it, as any damage to sensor wires and itself will require complete change out. Generally after cleaning the sensor, check engine light will go off.

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