

Why Is My Check Engine Light Flashing?

by Virginia A. Gorg


The check-engine light may be a graphic of an engine or similar icon, or it may contain the words "check engine" or "service engine." In some vehicles, a red check-engine light means the car needs absolute immediate attention while a yellow check-engine light means you need to make an appointment soon. Either way, you should know the location of the light and periodically glance at it to ensure its status. The light is used to indicate powertrain problems that are associated with your vehicle's emissions system. (The powertrain is the engine, transmission and other power parts of your vehicle.)

Flashing Light

Typically, a flashing light is more serious than a solid check-engine light. The flashing light is meant to alert you that you may have a misfire in your engine that will cause catalytic converter damage if you leave the problem unresolved. Replacing a catalytic converter can be costly, so have the engine checked as soon as possible by a certified mechanic.


A flashing check-engine light generally indicates that there is a failure in the emission control system. The emission control system contains an array of sensors that work to reduce the amount of pollution released into the air. An oxygen sensor reads the air and fuel mixture and lights up when it is out of range. The acceptable range is between 50 millivolts and 800 mV. If the check-engine light is flashing, you should visit your mechanic or dealer as soon as possible.

Loose Gas Cap

A gas cap that isn't twisted on tight enough may cause the check engine light to illuminate, but it won't flash. Try tightening the gas cap and watch the light. In many cases, it will turn off because the problem has been corrected. If the light stays on for more than a day or two, have your mechanic run an on-board diagnostic (OBD) to see if there is a code in the system indicating a serious problem. Your mechanic can reset the light to off if the problem was a loose gas cap.

Spark Plug Wires

As spark plug wires age, they can become brittle and crack, causing an electrical misfire. Your check engine light might turn on and stay lit. If this happens, go home as soon as possible, turn off your engine, and inspect the wires. If the wires are brittle and cracked, you need to replace them. If your check engine light stays on after the wires are replaced, have your mechanic run an OBD.

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