Why Is My Check Engine Light On?

One of the most commonly asked question among drivers is, “Why is my check engine light on”?  Although this is a simple question to ask, it’s not always as simple to answer.

All of our vehicles are equipped with a computerized engine management system (ECM) and the check engine light is a part of this system.  The ECM alerts us to possible problems inside the engine or inside the transmission that have an impact on the emissions system.  Check engine lights may be a graphic of an engine or a similar icon.  It can also be words, “check engine” or “service engine”.  Some vehicles use a yellow check engine light as a caution light that tells you to have your vehicle checked soon and a red check engine light that means your vehicle needs immediate attention.  Every car’s display is different, so it’s a good idea to make yourself familiar with how your particular make and model of vehicle works.  The check engine light is usually amber or red in color and has two stages, a steady light or a flashing light.  A steady check engine light signals minor problems, while a flashing check engine light usually means there is a serious problem in the ECM.

The cause of why your check engine light is on depends on your particular issue, but here are some general malfunctions that cause the check engine light to come on.

• A misfire in your engine.  A misfire can cause catalytic converter damage if it’s not resolved quickly.  The catalytic convertor works to reduce exhaust gases.  It converts carbon monoxide and other harmful materials into harmless compounds.  Replacing a catalytic converter can be costly, so have the engine checked as soon as possible by a certified mechanic.
• A failure in the emission control system.  The emission control system contains many active sensors that work to reduce the amount of pollution released into the air.  One of those sensors is an oxygen sensor that reads the air and fuel mixture.  If that mixture is out of the acceptable range or if you have  a faulty sensor, it won’t provide the correct data to the computer and the check engine light will go on.
• Brittle, cracked or worn spark plugs.  Worn spark plug wires can lead to an electric misfire inside the engine.  If the wires are worn out, they should be changed as soon as possible.
• A loose gas cap.  When it’s loose or cracked, fuel vapors leak out and can throw off the whole fuel system.  Sometimes when the cap is put on incorrectly the check engine light will come on.  If the light stays on for more than a day or two, have your mechanic run an on-board diagnostic to see if there is a code in the system indicating a more serious problem.

Check engine lights help you and your mechanic to keep your car running smoothly.  So the next time your check engine light goes on, don’t ignore it.  Come in and see us or call (303) 691-2760 and let us help.