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Why does my Check Engine Light Keep Coming ON?


The Check Engine light usually does NOT come ON without good reason! If it keeps coming back ON, this means that you still have a problem that was not solved! Find ANOTHER qualified mechanic to check for the codes in the Evaporative System. You can also try getting a brand-new gas cap.

You can also take your car to the Auto Zone and they will scan the computer code for free. Any auto parts store or a car dealer can check the code as well (call them to verify). After this, take the code to the mechanic and ask him to check that particular issue.

Getting an OBD II reader yourself is not a bad idea as well. They are NOT expensive and could save you a trip to the auto part store! This particular scan tool from BlueDriver (paid link) is wireless and BlueTooth enabled. It will show you information right on the smartphone.

This handy tool is especially useful if your Check Engine light lights up on an intermittent basis. It will allow you to “catch” the codes quicker before the light goes out again.

My check engine light keeps coming ON and OFF!

Check Engine light comes ON and stays ON if any kind of problem that could cause increased emissions is noticed by your onboard computer. There could also be a problem with a sensor that failed and in this case, the computer has NO accurate reading and brings up the Check Engine light.

Once the problem is fixed, the Check Engine light should go OFF on its own after about 10-20 miles. If it doesn’t go away or comes back ON, there is still something else wrong in your vehicle that needs to be addressed. The most simple thing you can check for is a properly closed gas cap or if the gas cap is damaged.

What is the most common reason for Check Engine light?

The most common reason for Check Engine light is damaged, improperly screwed on, or even completely missing, gas cap. The second most common reason is the oxygen sensor that is failing.

Here is a list of possible problems why the Check Engine light would come ON:

#1. Gas cap

Your gas cap could be cracked, loose, or have a worn-out seal around the cap. An improperly sealed gas tank will cause the fuel to evaporate while creating an EVAP (or Evaporative Emission Control System) leak.

The computer will sense improper pressure in your fuel tank and a Check Engine light will pop up on your dash!

#2. Failing oxygen sensor

It’s possible that an oxygen sensor has failed and needs to be replaced. If your issue occurs right after you leave a service station, have a friend check out your sensors for being unplugged.

#3. Evaporative vent solenoid

Solenoid’s filter could get filled with dirt and debris, therefore the tank will not vent properly. In this case, the solenoid needs to be replaced.

#4. Ignition coils

A faulty ignition coil can cause irregular sparks in your spark plugs which will lead to engine misfiring. If one of the cylinders is not firing correctly, your car will be jerking or vibrating as you drive at normal speeds.

Failed ignition coils will send a misfire code.

#5. Worn-out or fouled spark plugs

Worn-out, improperly installed, or torqued-down spark plugs could leak air and cause an air gap. This could lead to cylinder misfiring and filling your exhaust system with unburned fuel.

Once unburned fuel gets to the catalytic converter, it will overheat and start melting.

#6. Engine misfire

Anything that causes the cylinder not to fire can trigger the misfire code. The most common reasons for misfiring include incomplete combustion inside of spark plug or a clogged fuel injector.

Engine misfire can result in increased emissions and a damaged catalytic converter.

#7. Failing catalytic converter

When damage is already done to the catalytic converter, you should NOT be driving your car at all and taking it to the service station ASAP! Replacing a catalytic converter or multiple converters is extremely expensive and it should not be taken lightly.

If you notice that your Check Engine light is flashing stop the car and have it towed to the nearest service station!

Is your light steady ON/OFF or flashing?

Another thing to be on the lookout for is if the light is steady ON or if is it flashing.

If your light is NOT just going ON and OFF, but is flashing repeatedly, this is a critical situation which will cause big damage to your emission system if you keep on driving.

Usually, it means that you have a problem with the catalytic converter (or converters) and may be facing a very expensive fix.

The reason for intermittent Check Engine light could also be a corroded connector or bad sensor. If sensor wiring is damaged or you have a loose wire, this could also be a reason for this light to come ON, and later come OFF.

  • Light will generally come OFF if the computer senses that the problem is fixed.
  • It will come back ON again if the computer cannot get any response from the sensor (or the sensor is actually working and notifying it of a problem).

There are a lot of wires involved in a car, so better start diagnosing the problem codes.

Check Engine light could mean a really simple fix, but ignoring it for too long can turn a $100 problem into a $5000 problem!

The best way to find out what is wrong with your car is to get an OBD reading and full diagnostic analysis to figure out which exactly part is not working.

Don’t wait, check your car as soon as possible:

Attention! This article is for informational purposes ONLY and is NOT a replacement for professional advice! ALWAYS consult your local specialist for an appropriate solution to your problem. All statements, prices, contact information, recommendations, and reviews contained herein came from sources that we believe to be reliable, but the accuracy or completeness thereof is not guaranteed. Please contact the service provider for complete details and updates.

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