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Check Engine Light On? 5 Common Reasons

By Hanna H.
Here are the five most common causes of the check engine light coming on, none of them catastrophic to your day nor your wallet:

1. Loose or Faulty Gas Cap: This is the easiest one to fix, and you can check for this yourself! The cap might be cracked. Seems minor right? And it is. Except that a malfunctioning, cracked or loose gas cap mean fuel vapors are escaping and this can actually throw the whole fuel system off. So, if you think this might be the case, replace it and see if the problem is solved, Or bring your car in for a Murrieta Check Engine Light Diagnosis. If this is the verdict, we will replace the cap for you. The light goes off, and with a minor charge, and you are on your way.

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SMOG, Diesel Experts, Auto Check,
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Filed Under: Car Maintenance, Check Engine Light
Tagged With: Check-Engine-Light, How-to, Symptoms
Check Engine Light Diagnosis
2. Worn out Spark Plugs: The spark plugs seal the combustion chamber in your car and initiates combustion in your engine. When the plugs fail, they misfire. You’ll feel a jump when you accelerate if your plugs are failing. Plugs can last a pretty long time in a car; in newer cars even up to 100,000 miles. When your plugs fail you need to get them replaced right away. This is an easy and inexpensive fix, and your car will run better and not be jerky when you accelerate, so get it done.

3. Bad Mass Airflow Sensor: The mass airflow sensor tells the car's computer to add the proper amount of fuel based on the air coming through to the engine. A faulty one can increase emissions, cause the car to stall, and decrease your gas mileage. So, if your car has been stalling before the check engine light came on, this is most likely the problem, although this will not always happen before the check engine light comes on. This failure is also something that is easily avoided if you bring your car in for regular maintenance.  

4. Bad Oxygen Sensor: An oxygen sensor monitors the amount of unburned oxygen in the exhaust. If the sensor is not functioning properly, it doesn’t provide the right information to the car’s computer and ultimately causes a decrease in gas mileage – which is why it’s a good thing that you know this is happening. No need to flush money down the drain by getting lousy gas mileage. Most cars have more than one oxygen sensor and the diagnostic computer will tell us which one needs to be replaced. 

It’s also important to replace a faulty oxygen sensor because not replacing one that is faulty can eventually lead to a broken catalytic converter, and this is a very expensive repair. So better a much, much less expensive sensor replacement now, than replacing an expensive catalytic converter later.

5. Bad Catalytic Converter: This is not such good news. You usually will notice something is going wrong with the car before the check engine light comes on in this instance. You will definitely notice a decrease in gas mileage or your car might not even go any faster when you push the gas pedal.

What does a catalytic converter do? It works to reduce exhaust gases. It converts carbon monoxide and other harmful materials into harmless compounds (which is what the State of California loves, right?) So a failed catalytic converter stops converting carbon monoxide into other harmless compounds. Catalytic converters shouldn’t fail if you regularly maintain your car.  

We can replace the catalytic converter for you if it’s necessary, but it is an expensive replacement. So please, bring your car in for regular maintenance and particularly if you notice a decrease in gas mileage before we have to go to this extreme. 

Of course, there are other reasons your check engine light might come on. But among the possible causes that a Murrieta check engine light turns on, the above are the most common. So next time your light comes on, be sure to take care of it right away and visit us for a Murrieta Check Engine Light Diagnosis.

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