Learn the Top 5 Reasons Your Check Engine Light May Be On

The Check Engine Light (CEL) is never good news. At the very least it means you'll need to service the engine soon, or check some of the auxiliary systems. You may want to ignore it, but the light means there's a problem that will only get worse the longer you leave it unchecked. Here at AutoZone, we're pretty familiar with the light, so we've rounded up the 5 most common causes and everything else you need to know when you're wondering, "Why is my Check Engine Light on?"

Is the CEL Lit or Flashing?

If the light is steadily lit, that means that one of your engine sensors picked up suspicious reading. This can indicate a problem with an engine component, or with one of the sensors. You can still drive with the light illuminated, but you should get it checked out as soon as possible. If the light flashes, that means you need to pull over immediately as your vehicle has a serious issue that could cause imminent damage.

Can I Check My Own Light?

You can. All that you need to check your own light is an OBD-II reader, which can pull codes that help you find out what's wrong with your car. If you don't have a code reader, keep reading to learn the most common causes, and then bring your car to your local AutoZone to find out why your Check Engine Light is on.

Check Your Own CEL

5 Reasons You May Have a Check Engine Light On

1

Your oxygen (O2) sensor needs to be replaced

Your oxygen sensor measures the amount of unburned oxygen in your vehicle's exhaust system.

What happens if I don't replace it?

  • Your engine will burn more fuel than needed
  • You will lose fuel economy, and get fewer miles per gallon
  • Faulty sensor(s) can cause damage to your spark plugs and catalytic converter
2

Gas cap is loose, damaged, or missing

Your gas cap seals the fuel system and helps maintain pressure within the fuel tank. It also prevents gasoline fumes (hydrocarbons) from being released into the atmosphere while you aren't driving your car.

What happens if I don't replace it?

  • You can lose fuel through evaporation
  • You may take more trips to the gas pump
3

You have a bad catalytic converter

Your catalytic converter helps protect our environment by converting harmful carbon monoxide into carbon dioxide. Damage usually occurs due to neglected maintenance (like the parts in reasons # 1, 4, and 5).

What happens if I don't replace it?

  • Your vehicle will not pass an emissions test
  • You will experience reduced performance and fuel economy
  • Your car may run at a higher temperature
4

It's time to replace your Mass Airflow Sensor (MAF)

Your mass airflow sensor measures the amount of air entering the engine to determine how much fuel is needed to run your engine efficiently.

What happens if I don't replace it?

  • Faulty sensors can cause damage to spark plugs, O2 sensors or catalytic converter
  • You will experience reduced performance and fuel economy
5

Your vehicle needs new Spark Plugs or Plug Wires

Your spark plugs ignite the air/fuel mixture in the combustion chamber of your vehicle. The spark plug wires deliver the spark from the ignition coil to the spark plugs.

What happens if I don't replace it?

  • You will experience poor performance (reduced power, engine missing) and reduced fuel economy
  • Worn plugs and plug wires can cause clogged catalytic converter or damage to ignition coils and O2 sensors

These are the most common reasons, but there are others too. Finding out why your Check Engine Light is on may help you save gas and avoid more problems down the road. Get in the Zone.

The AutoZone Fix Finder

Fix Finder is an easy-to-use tool to troubleshoot why your Check Engine Light is on using an extensive database of repair solutions from ASE certified mechanics to help you find the most likely fix.

How does AutoZone Fix Finder work?

  • Fix Finder reads diagnostic trouble codes from your vehicle’s onboard diagnostic system, and pulls your vehicle information and mileage.
  • This data is analyzed to give you vehicle-specific fix solutions that have been verified from the records of over 5.5 million ASE-Certified technicians.
  • AutoZone gives you a FREE, easy-to-read MYZONE HEALTH REPORT, which includes relevant codes, and details the action that needs to be taken.

Let us help you find out if the problem is simple or serious

Your Check Engine Light may be indicating a simple problem that’s easy to fix—such as a loose gas cap that needs to be replaced. It could also be a warning of a serious problem that could damage your engine components.

Your Check Engine Light blinks or glows depending on what’s wrong with your vehicle. A flashing Check Engine Light indicates that your vehicle’s engine is in serious trouble, whereas a steadily lit one means less urgent service is needed. Regardless, it’s easy to find out what the issue is, and taking care of it quickly can save you money, and prevent further damage down to the road.


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