Common Reasons Why Your Check Engine Light Is On

April 16th, 2015

An illuminated check engine light is a signal from the vehicle's engine computer that something is wrong. Many people worry that it means a costly repair is needed, but that's not always the case. Here are some of the common reasons why a check engine light turns on.

Loose or Broken Gas Cap

Probably the most common reason for an illuminated check engine light is a gas cap that hasn't been screwed on tightly. When it's loose or cracked, fuel vapors leak out and can throw the whole fuel system off. This also happens to be the easiest thing to repair—just give the gas cap a few turns, and drive around for a few miles to see if the check engine light turns off. In some cases, the gas cap is cracked and needs to be replaced at an auto repair shop.

Faulty Oxygen Sensor

The oxygen sensors help the vehicle's on-board computer determine how much fuel it should be burned by monitoring the unburned oxygen from the exhaust. Over time, oxygen sensors wear out and become covered in oil ash, reducing their ability to provide accurate readings. A faulty oxygen sensor means it's not providing the right data to the computer, which increases vehicle emissions and decreases fuel efficiency.

Replace Catalytic Convertor

Catalytic converters transform harmful carbon monoxide emissions into compounds that are friendlier to the environment. If the catalytic convertor isn't working it will decrease your fuel efficiency and increase vehicle emissions.

Malfunctioning Mass Airflow Sensor

This important component tells the on-board computer how much fuel to add based on how much air is coming into the engine. If your vehicle is experiencing reduced fuel economy or is starting to stall, it may have a malfunctioning mass air flow sensor.

Bad Spark Plugs or Wires

Failing spark plugs cause the engine to misfire, which negatively affects both emissions and efficiency.

There are many other possible reasons for the check engine light to come on, but these are the most common. When the check engine light comes on, many people do nothing because they fear an expensive repair bill. Last April, during the Car Care Council's National Car Care Month inspection checks, 13% of vehicles inspected had the check engine light on. But ignoring it can end up causing more costly damage.

When your check engine light comes on bring your vehicle to Dekalb Tire and Automotive Service. Our trusted mechanics will run a free diagnostic computer test to determine what triggered the light.

  Posted in: Auto Repair 101