There’s one little yellow light that strikes fear in the heart of every driver. It casts a shadow of doubt over your whole vehicle. Will this be something straightforward or will the repair bill put you in debt?

The Check Engine Light has long puzzled drivers with its vague warning. When it illuminates, it's unclear if you should continue driving or get your car towed. Here’s everything you’ve wanted to know about the Check Engine Light:

What the Check Engine Light Does

The Check Engine Light has one purpose: to tell you when you have a problem. That’s all. It doesn’t tell you what the problem is; a technician will have to perform a diagnostic scan to check the affected system. It only indicates that something isn’t working properly.

The Check Engine Light is also known as a malfunction indicator light. It’s shaped like a motor and is yellow in color. Most vehicle systems run self tests under certain operating conditions, and the results are reported to their respective control modules. If a self test fails under certain parameters, your car’s Check Engine Light will come on. It could be an engine, transmission, or emissions system that didn’t pass the test.

What Does the Check Engine Light Mean?

There are two different ways the Check Engine Light can come on: solid or flashing. They mean two different things.

If the engine light comes on and flashes, that indicates an immediate concern. You need to find a safe place to pull over and turn your vehicle off. You may want to consider getting it towed to the shop. A technician needs to diagnose the concern at the absolute earliest convenience to prevent damage to your car. A flashing Check Engine Light is serious business.

If the engine light comes on solid, it may still be a reason for concern, however it doesn’t immediately need to strike fear in your heart. A solid Check Engine Light can mean something like a loose gas cap, or it can indicate a more in-depth problem like a fuel, timing, or transmission issue. Get your car diagnosed, although the urgency isn’t the same as if the light was flashing at you.

Common Reasons the Check Engine Light Comes On

The reason for an engine light can be a risk of catastrophic failure or something requiring immediate attention, or it could be nothing at all. As the car’s systems run self-tests, it is possible that a test fails and the engine light comes on, and the next test passes. The Check Engine Light may not turn off as soon as it passes, and it may not even turn off until a technician clears the code even though there is no repair required at all. Common reasons for the Check Engine Light are:

  • The gas cap was left loose when refuelling
  • Emissions-related sensors, such as oxygen sensors, have failed
  • Engine timing problems, most commonly with variable valve timing
  • Transmission failure codes
  • Engine misfire codes
  • Catalytic converter problems

There are literally dozens, if not hundreds, of other reasons for the Check Engine Light to come on. If it illuminates, have it checked out expediently. Don’t take unnecessary chances if it feels like the vehicle is not operating in a safe manner. Have your vehicle towed to the shop if you don’t feel safe driving it. If the Check Engine Light is flashing, it is in your best interest to cease driving until the light has been diagnosed and repaired.

This article originally appeared on YourMechanic.com as The Check Engine Light Demystified and was authored by Jason Unrau.


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