check engine light

Automotive Diagnosis: 10 Most Common Reasons for Check Engine Light

Check engine light related problems will cost you about $357 to fix. If the cause is not identified and resolved in good time, it could cost you more.

While some issues require you to take the car to a mechanic, some are relatively easy to sort out by yourself.

Knowing the most common reasons for a check engine light can give you peace of mind and in some instances, save you money and time.

Below are the most common reasons for check engine light.

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1. Air Mass Flow Sensor Failure

The MAF signals the car’s computer to release the correct amount of fuel to match the amount of air coming through the engine.

The Mass Flow Sensor is most vulnerable in dry and dusty summer roads. The same goes for snowy and icy roads.

Problems with the MAF can be prevented by keeping the air filter clean. Generally, you should replace the air filter yearly.

A faulty MAF can cause the car to stall, increase emissions and decrease the gas mileage. You might also notice a rough idling.

2. Faulty Spark Plugs and Ignition Oils

Spark plugs seal the combustion chamber and allow a spark to jump across and initiate combustion in your engine.

When they malfunction, the plugs misfire. Your car then begins to accelerate with sudden jolts. This is dangerous and can cause an accident. Learn more about what you should do if you find yourself in a car accident.

Spark plugs are part of your car’s maintenance regimen, so they get checked at each service. However, they might malfunction in between services, which warrants a replacement.

3. Failing Catalytic Converter

The function of the catalytic converter is to reduce exhaust gasses. It converts carbon monoxide into harmless compounds.

When it starts failing, one of the things you notice is a decrease in gas mileage or failure to accelerate when you push the gas.

The main causes of failure in sparkplugs include faulty spark plugs or a malfunctioning oxygen sensor.

You can still run your car if the catalytic converter is not totally plugged. However, it is important to have it checked.

4. Faulty or Loose Gas Cap

When your gas cap is loose, fuel vapors start to escape, throwing off your entire fuel system. This results in an increase in emissions and a reduction in gas mileage.

Anytime you get an error leading you to the gas cap, it means the cap was not tightened well enough, or it has cracks on it.

If the check engine light comes on and the car is not jerking, this is the first thing to check.

While it’s in itself not car threatening, taking care of it immediately will improve gas mileage.

To start, remove it and check for cracks then put it back tightly and observe if the check engine light goes off. If it is cracked or otherwise damaged, have it replaced.

5. Malfunctioning Oxygen Sensors

The oxygen sensor monitors the unburned oxygen from the exhaust, to see how much fuel is burned.

If it’s not functioning correctly, it provides inaccurate data to the computer, causing a decrease in gas mileage.

Most cars have two to four sensors. If there is a problem, the scanner can give you a code to notify you which of them requires replacement.

With time, the sensors get covered in oil ash which reduces their ability to function. This increases emissions and reduces gas mileage.

If you do not replace the sensors in good time, the catalytic converter could get damaged.

6. Faulty Spark Plug Wires

Spark plug wires transfer energy from the coils to the plugs.

Without this, the air mixture and oil in the cylinders cannot ignite. Many cars use a single wire per cylinder, but there are models with two plugs per cylinder. The latter comes with two wires as well.

Some of the symptoms of faulty spark plug wires is a drop in engine performance, a rough idle and lower gas mileage.

7. Car Alarms Are Common Reasons for Check Engine Light 

If incorrectly installed, an after-market alarm system can mess your car.
It can prevent the car from starting, drain the battery and trigger the check engine light.

To prevent this, have the alarm system professionally installed the first time around. It is always important to work with a reputable installer to ensure that you get the best service. 

If it’s been incorrectly installed, have a professionally yank it off and reinstall it properly.

8. Dead Battery

A dying battery will not adequately power your car’s computer. As a result, it will generate an error code triggering a check engine light.

Fortunately, most batteries today last much longer and are maintenance free. Another good thing is that replacing a dead battery with a new one does not require a trip to your mechanic.

9. Malfunctioning Thermostat

Your car’s thermostat works in the same way as your house’s thermostat.

It monitors the engine’s temperature and heats or cools it if it detects a change. Your car’s thermostat varies temperatures by regulating the flow of coolant into the engine.

When you fail to change the coolant regularly, it accumulates dirt and little pieces of debris over time.

When the coolant flows over the thermostat, these bits and dirt can corrode its surface causing it to fail.

10. Fuel Injectors

Fuel injectors can become clogged with dirt and oil, meaning there will be difficulties getting gas to the engine.

If the fuel injectors malfunction, you will notice that your car lags when you push down on the accelerator.

To correct this, flush the system or try a fuel injector cleaner.

 DIY or Mechanic?

The above are the most common reasons for check engine light.

If you have some mechanic skills, a DIY can obviously save you some costs.
However, be objective about your skill set and go to the repair shop if you suspect a job might be difficult to handle.

Do you want to beef up your car fixing skills? Check out our blog for some expert DIY diagnostic tips.