Top 5 Reasons 'Check Engine' Lights Up

This content is provided courtesy of USAA.

A bright check engine light on your dashboard can indicate a variety of problems. Some may be simple to fix, such as a loose gas cap, while others, such as a failed catalytic converter, can be expensive to repair.

Often, your car may seem to be running fine even when the light is on, but don't ignore it: Immediately head to a mechanic to check out the cause. You also may be able to get a free check at some national auto parts stores.

Here are the top five reasons that a check engine light goes on and the estimated repair costs, according to CarMd.com:

1. A faulty oxygen sensor, which can reduce gas mileage up to 40%. It costs about $200 or less to replace.
2. A loose, damaged or missing gas cap — did you just refuel? Sometimes all it takes is tightening the cap. But if you need to replace it, the cost can be less than $10.
3. A bad catalytic converter, which can cost $1,000 or more to replace.
4. A malfunctioning mass airflow sensor, which can cause fuel economy to drop up to 25%. The sensor costs $375 or more to fix, depending on the vehicle.
5. A bad spark plug, which eventually can damage the catalytic converter. Changing a plug yourself can cost less than $10. As part of an engine tuneup in a shop, it can run $200 or more.