Why is My Check Engine Light On?

If your check engine light is on, don't panic. In this guide, you will learn what it means when the check engine light stays on or flashes and how to reset it yourself. 

What does it mean when the check engine light stays on? 

check engine light on
Check engine light, also known as Service Engine Soon light. 

When the check engine light comes on and stays on, it means the On-Board Diagnostic (OBD) system has detected a problem with the emission system, engine performance, and in some cases, the transmsion. A fault code will get stored in the Engine Control Unit (ECU) and can be read with an OBD-II scanner. 

The most common problems that trigger the check engine light are worn spark plugs, bad mass flow sensor (MAF), failed oxygen (O2) sensor, and loose gas cap. These problems are easy to repair by a DIYer and can cost anywhere from $10 to $150 in most cases. 


To find out why your check engine light has come on, you need to use an OBD2 scanner to retrieve the Diagnostic Trouble Codes (DTCs). This is a straightforward procedure that takes about five minutes.

How to Reset Check Engine Light Yourself

Follow these steps to learn how to read and reset the check engine light on any vehicle: 

  1. Locate the diagnostic port under the dashboard on the driver's side. All cars have this port. Sometimes it is hidden in the fuse box on the driver's side, but in most cases, the port is right under the dashboard. obd ii port


  2. Plugin your OBD-II scannerdiagnose check engine light for free yourself


  3. Turn on the ignition but do not start the engine. On cars with the Start/Stop button, you need to press the button without pressing the brake pedal. 

    turn on ignition

  4. Your scanner will take a minute to communicate with the on-board diagnostic system. 
  5. Select OBD-II, then Read Codes from the main menu. read check engine codes free
  6. Write down all the codes. Pay attention if they are Stored or Present. 
  7. Once you fix all the problems that triggered the fault codes, come back to the main menu and select Clear Fault codes, then OK. That's it. We don't recommend clearing fault codes without fixing the problems that triggered the codes. If you clear the codes without fixing the problem, the check engine light will come back on. Check engine  codes

Stored codes mean that an issue was detected in the past, but currently, it is no longer an issue. These codes will typically reset on their own after a few days of driving. 

Preset codes mean that the problem is current, and it needs to be addressed.

You may be tempted to erase these codes, but clearing present codes without fixing the car is not a solution. The codes will return either as soon as you start the engine or take up to two days, but they will eventually return if your car problem isn't fixed. 

What is the best tool to reset the check engine light? 

OBD II scanner

To find out why your check engine light is on, you will need an OBD-II scanner. Many auto parts stores will let you borrow a scanner for free, or you can buy an inexpensive OBD-II scanner and keep it in your glove box. We are using a sophisticated scanner, but honestly, even a $15 scanner will retrieve check engine codes. 

If you don't want to buy a scanner, here are some auto part stores that will scan your car for free or let you borrow a scanner. 

  1. Aamco Auto Repair Center
  2. Advance Auto Parts
  3. AutoZone
  4. O'Reilly Auto Parts
  5. Pep Boys Auto Parts
  6. Napa 

Click on any of these stores to find a location near you to check your engine light for free. 

What does it mean when the check engine light is flashing? 

If your check engine light is flashing on and off, it means that the engine is missfiring. This condition is typically caused by a bad spark plug, ignition coil, clogged catalytic converter, or blown head gasket.

Read the codes with an OBD-II scanner to find out why your check engine light is flashing. 

If your check engine light comes on, don't ignore it but read the codes as soon as possible. If the check engine light is flashing, driving with the check engine light can cause serious engine problems. 

Can I drive with the check engine light on? 

Don't ignore the check engine light. The codes stored on the On-Board Diagnostic (OBD) system can help you find out what is wrong with your car. 

Even if you don't plan on fixing your car yourself, knowing why your check engine light is on can help you feel more confident when you talk to your mechanic.  On some models, the check engine light may be referred to as the service engine soon light. 

By  YOUCANIC Automotive Experts

Published on: Thursday, January 23, 2020.
Updated on: Monday, November 23, 2020