Why is My Check Engine Light On?

Reading Time: 4 minutescheck engine warning light

Seeing a car’s check engine light illuminated on the dashboard can cast a feeling of dread for drivers who equate the symbol with costly repairs. The warning light indicates a malfunction with one of the vehicle’s systems, but even minor problems can trigger an alert.

If your check engine light is flashing, there is a serious issue, and you should turn off the engine as soon as it’s safe to get off the road. After stopping your car, you will want to know why your check engine light is on in the first place, and how to fix it.

What Makes a Check Engine Light Come On

Modern cars have a check engine light to notify the driver that something isn’t functioning the way it should. Known technically as the malfunction indicator lamp (MIL), this warning light in your instrument cluster is in the shape of a car engine. The light can be orange, red, or yellow, depending on your vehicle. Some models display “check engine” with the engine outline.

Sensors monitor the many complex functions in your engine. The automobile’s system receives information from the sensors to self-diagnose internal problems. Carmakers use the second generation of standardized on-board diagnostics, known as OBD-II, for model years 1996 and later. Older cars use an earlier iteration of the OBD protocol.

If sensors detect information that falls outside a normal range, the system creates an OBD-II code, which activates the warning light.

  • Check engine light on: When the check engine light turns on and stays on, the issue is typically related to emissions systems or some safety-related faults.
  • Check engine light blinking: A check engine light flashing or blinking indicates an issue severe enough to cause damage to critical systems like the catalytic converter, internal engine fuel, or air induction systems.

Don’t confuse the check engine light with your car’s maintenance required or service required light. This service notification is shaped like a wrench and alerts you that an oil change or other scheduled maintenance is due.

Diagnose Check Engine Light Problems

check engine warning light

Your vehicle’s diagnostic codes are accessed using an OBD-II scanner or reader that connects to a 16-prong port usually located beneath the steering column. You have three options to obtain the code that triggered the check engine light.

  • Find a car repair shop that will run their scanners to diagnose the issue for a fee. Shops usually waive diagnostic fees if you have the corrective service done at that location.
  • Go to an auto parts store and have the code read at no charge. If the code indicates a minor problem, you might be able to fix it yourself.
  • Purchase an OBD scanner at your auto parts store or online. A good-quality reader can cost less than $50. Also, hundreds of OBD-II apps are available for your smartphone, and the car’s Bluetooth is used to access diagnostic codes. These wireless options are available at every price point, including free. In some cases, you might get what you pay for.

Even if you don’t do the repairs yourself, obtaining codes is beneficial if you want to check against what your mechanic said. It helps ensure that the service center addresses the right issue with your car.

Check Diagnostic Codes

Every driver should understand the meaning of warning lights that signal problems with their vehicles. The owner’s manual will illustrate where the symbols appear on your gauge panel and help you interpret their meaning. Take this information seriously and pay attention to any warning light that comes on.

It’s never a good idea to ignore a check engine light. It’s wise to take the car to a mechanic when the light comes on and address the problem. If you do your own investigation and determine the code that causes the warning, search a list of OBD-II codes to tell you which specific component has an issue.

Not every check engine warning light generates big bills. Sometimes the problem is as simple as tightening the fuel cap. Others, especially when accompanied by oil or temperature warning lights, can mean more significant issues at hand. However, if the oil or temperature lights come on, you should immediately stop the vehicle in a safe area and turn off the engine. Oil starvation or high engine temperature conditions can irreparably damage the engine and other components.

Turn Off Engine Warning Light

If your state requires an annual vehicle inspection, you’ll need to take care of the problem behind the check engine light beforehand. A car will not pass inspection if the check engine light is steady or flashing.

If a mechanic fixes the cause of the check engine warning on your car, they should reset the diagnostic system to clear any codes. Most OBD scanners that you can buy will clear and reset codes that make the check engine light come on, even if you haven’t fixed the issue. The light will come on again, and ignoring the root cause can create even more problems and more significant expenses.

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    Chris Hardesty

    Chris Hardesty is an author specializing in electric vehicles and general advice related to car ownership. His 25-year journalism career includes leading editorial research at The News & Observer in North Carolina, The Mercury News in California, and Newsday in New York. After that, he was an online news editor at The Wall Street Journal before moving to the Atlanta area. He didn’t have a vehicle while living in New York City, but Chris has found the Chrysler Pacifica is well-suited for toting children – and lumber – in his new suburban life.

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