5 Common Reasons Your Check Engine Light Is On

Why is my check engine light on?

We’ve all been there before. You’re driving along when out of the blue the dreaded check engine light comes on. You feel immediate panic. You worry it’s an expensive repair, and start budgeting things out in your head. The good news, often times the check engine light is just a warning before major issues arise. The ASE certified technicians at Metro Transmission and Automotive have seen thousands of cars come through our shop bay, and we’ve compiled a short list of the most common issues we see when diagnosing a check engine light warning.

5 Common Reasons For Your Check Engine Light To Come On

  • The Oxygen (o2) Sensor
  • Loose or Damaged Gas Cap
  • Spark Plugs and Wires
  • Catalytic Convertor
  • Mass Airflow Sensor

Oxygen (02) Sensor

The O2 Sensor was developed in the late 1960’s and can be found in all cars from the 1980’s and newer. Data from the sensor is sent to your vehicles internal computer where it can regulate the air and fuel ratio.  Although your car will still operate after an oxygen sensor goes bad, it can lead to poor gas mileage and further damage the components of your engine.

Loose or Damaged Gas Cap

A loose or damaged gas cap is one of the most common causes of a check engine light warning.  Taking the cap off while the car is running, not tightening the cap down enough, and damage to the cap itself can all trigger your check engine light.

Spark Plugs and Wires

It’s not uncommon for spark plugs and wires to fail on a vehicle.  Older vehicle plugs and wires can last around 30,000 miles, while newer vehicles can last as long as 100,000 miles.  If you’ve noticed a decrease in your vehicle’s performance with the appearance of you check engine light, the plugs and wires could be the reason.

Mass Airflow Sensor (MAF Sensor)

The most common reason a check engine light is triggered because of the MAF Sensor is due to improper installation of an air filter, or because your air filter life has expired.  Depending on your location, it’s best to change your air filter around once every 12 months.

When it comes to a check engine light warning, the Time To Act Is Now!

Sometimes a check engine light is something simple like a loose gas cap, but should always be treated as if it is something major. We recommend bringing your vehicle in for diagnostics as soon as possible. Ignoring the check engine light can lead to costly repairs or possible vehicle breakdown, and that’s never fun! Beyond avoiding major repairs, it can also lower your stress levels by knowing exactly what is wrong with your vehicle.

If you have any questions on check engine lights, or would like to schedule an appointment to have your vehicle scanned, give us a call today at (760) 471-0223.  Our friendly and knowledgeable ASE Certified Technicians will be happy to assist you!

Metro Transmission

Metro Transmission

The ASE Certified Mechanics at Metro Transmission and Automotive have over 100 years of combined experience. We're a full service, AAA Approved Auto Repair Shop, conveniently located in San Marcos, CA off Highway 78.

Award Winning Auto Repair Services

A Name You Can Trust



The most frequently asked questions about our business and services
Click Here



Save money on our award winning services with special offers.
Click Here



See what our clients have to say about our auto repair services.
Click Here