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The check engine light can be an intimidating surprise. A number of questions immediately come to mind: What’s wrong with your car? Will it be expensive to fix? Can you fix it yourself, or will you have to bring your car to a mechanic? With the right tools and resources, you can quickly get to the root of the issue.

Why Did the Check Engine Light Illuminate?

First, think back to when the light came on. Was it just after you refueled or hit a pothole? Then, consider any other potential clues. Is there steam coming out from under the hood? Does the engine sound like a shaking box of hammers?

Generally speaking, the severity of the issue will dictate how promptly you must address the situation. Here’s how the check engine light (CEL) can help you understand whether you should drive straight to the garage, or take your car in when you have free time in a few days:

  • When you first start the engine, the check engine light (CEL) will illuminate for a few seconds during the system’s normal self-check process.

  • If the engine is not running properly, the electronic control unit (ECU) logs the issue and sets a “pending” diagnostic trouble code (DTC). If the condition persists, the ECU sets a “hard” DTC and puts the vehicle in “limp home” or “open loop” mode. The system illuminates the CEL, which is also called a malfunction indicator lamp (MIL).

  • If the CEL illuminates steadily, this means that there is a fault in the system, but it is still safe to drive. You may not notice a lack in performance, but the EPA estimates that some vehicles may suffer up to a 40 percent loss in fuel economy if the problem is serious.

  • If the ECU determines that the engine is running so poorly that it can damage the catalytic converter, the CEL will blink continuously. In this case, you’ll probably notice a serious decline in engine performance.

What’s Next?

There are a few issues that will cause the CEL to illuminate that can be fixed in your own driveway. For example, if you just refueled, the problem could be something as simple as a loose or broken gas cap, a quick and safe fix. A faulty temperature sensor or coolant leak could be causing your system to log engine temperature codes. Replacing an engine thermostat is within the realm of most DIYers.

On the other hand, if the check engine light comes up because of a heavy misfire or traction control system fault, or if the problem is under the vehicle or exceptionally deep in the engine, you might be better off letting the professionals have a look.

Check out all the maintenance parts available on NAPA Online or trust one of our 16,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on diagnosing a check engine light, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

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