Special Report

20 Most Common Problems Behind a Check Engine Light

Car owners are familiar with that dreaded feeling when the “check engine” indicator lights up on the dashboard display. It could be a minor issue, such as a loose gas cap, but it could also be something serious, like cylinder misfires that can do costly damage to the engine if left unattended. Engine problems can also decrease mileage efficiency and allow excess fuel vapors to escape into the atmosphere — even if you’re driving one of the most eco-friendly cars on the market

The check engine light, also known as the malfunction indicator lamp, is the result of an industry standard that began with the 1996 model year, according to automotive information provider Edmunds. Since then, new vehicles have been equipped with a universal on-board diagnostics system (OBD-II), accessed with a code reader which a mechanic plugs into a connector usually located near the base of the steering column. The code reader collects sensor-generated alphanumeric “trouble codes” that can identify numerous problems.

The way the check engine light works varies by vehicle. It can flash or stay illuminated. In some cases, the light changes from yellow to red or orange to indicate a more serious mechanical problem. 

Click here to see the 20 most common reasons for a check engine light.

Some cars also include a general maintenance reminder light in addition to the check engine warning. Refer to your manual to learn what these indicators mean — especially if you drive one of the new cars that are most likely to break down.

To determine the 20 most common reasons for a check engine light 24/7 Wall St. reviewed 2021 data from FIXD.com, which aggregates data from 18 million vehicles that detected and cleared engine codes from the FIXD OBD-II sensor in 2020. Vehicle repair data was obtained from CarMD’s 2021 Vehicle Health Index which lists the 10 most common classes of check-engine-light-related repairs in 2020, as well as the average cost to make the repair.