5 Reasons Your "Check Engine" Light Is On

You’ve seen it at some point or another: the dreaded “check engine” light on your car’s dashboard. Is there nothing to worry about? Or is it hinting at a big problem with a potentially expensive repair bill at the end of the tunnel?

If you’re like most car owners, you may not immediately know what the light is signaling.

We’re here to help you understand the five most common reasons why your “check engine” light may have activated.

1) Your gas cap is loose or damaged.

A loose or damaged gas cap can cause fuel vapors to leak, triggering system sensors and the “check engine” light to activate. Failure to replace your gas cap can result in your vehicle losing fuel through evaporation.

What you can do: First inspect your gas cap to see if it’s cracked or otherwise damaged. If it is, this is an easy, inexpensive replacement. To replace, simply unscrew the old gas cap and screw in the new one.

If you don’t see any cracks or damages, try unscrewing then retightening your gas cap. If the “check engine” light persists, you should consider having your mechanic inspect the issue.

2) Your oxygen sensor needs to be replaced.

Your oxygen sensor monitors the amount of unburned oxygen from your vehicle’s exhaust system. When in working order, the oxygen sensor optimizes the amount of fuel your engine needs to make your car’s miles per gallon (mpg) more efficient.

A defective oxygen sensor sabotages this purpose and can cause a 40% reduction in your car’s miles per gallon. Failure to replace a broken oxygen sensor can result in a defective catalytic converter (#5 on this list), with an upward cost of $2,000.

What you can do: While not as easy to replace as a broken gas cap, it’s still not impossible and many car owners DIY or take it to your local mechanic to have them replace.

3) Your spark plugs need to be replaced.

You’ve probably heard the metaphor “firing on all cylinders.” Well, your car’s spark plugs literally “fire on all cylinders.” Your car’s spark plugs provide the necessary “spark” to ignite the combustion in your engine’s cylinder head so that it can fire on all available cylinders. Faulty spark plugs can mean lots of wasted gas and reduced power for your vehicle.

What you can do: If you’re feeling particularly handy, you can replace the spark plugs yourself or take your car to get checked out by a mechanic.

4) Your Mass Airflow Sensor needs to be replaced.

The Mass Airflow Sensor regulates fuel injection to the engine by measuring current inflow of air to the engine. Defective sensors can spell doom for your car’s spark plugs, oxygen sensors, or catalytic converter, reducing your fuel economy and possibly causing your car to stall.

What you can do: Part replacement plus labor can cost between $200 and $300. While it’s not impossible to DIY, it may not be worth the time or effort. Have your mechanic replace your Mass Airflow Sensor instead.

5) Your catalytic converter needs to be replaced.

The catalytic converter transforms harmful carbon monoxide into harmless compounds to protect the environment. A failing catalytic converter will lead to reduced fuel economy and/or power.

What you can do: Unfortunately, this is both a complicated and expensive replacement (upwards of $2,000). A non-operable catalytic converter will eventually lead to your car’s inability to even run, so you should get this problem fixed by your mechanic as soon as possible.

Get help paying for part fixes and replacements

Unfortunately, the “check engine” light is inevitable in the life of car ownership and can spell a range of car problems from loose gas caps to busted catalytic converter that can drive up a hefty repair bill.

The good news is you don’t always have to face these bills alone. Those with Vehicle Service Contracts (VSCs) can get help with covered auto repair bills through their plan. Learn more about various VSC options to decide if they’re right for you before repair needs arise.