How to Reset an Engine Computer

by Jody L. Campbell

Any vehicle built from 1996 until now comes equipped with an on board diagnostics two (OBD II) computer system. Prior to that, some vehicles were equipped with an OBD computer system or none at all. With the implementation of computer systems in cars, they can now communicate to the driver by illuminating the malfunction indicator light (MIL), which triggers the "service engine soon" or "check engine" warning on the dashboard. Resetting the computer nowadays is getting easier and more affordable for the do-it-yourselfer.

How to Reset an Engine Computer

Locate the diagnostic link connector (DLC) under the driver's-side dashboard. This is a trapezoidal-shaped outlet the to which the plug of the code reader needs to attach. You may have to refer to your owner's manual for the location, as there is no universal spot for it. In some rare cases, it may be located on the passenger-side lower dash or behind the vehicle's ashtray. Once you've located the DLC, plug the code reader into it. The vehicle's battery will automatically power up the code reader.

Place the keys in the ignition and turn two clicks to activate the "Key On/Engine Off" mode. This will allow power to all the electrical components of the vehicle and illuminate all the lights on the dash, without the engine running.

Look at the menu screen on the code reader. There will be number of options to which you can manipulate the cursor by operating the up or down arrow buttons on the faceplate of the code reader. Using the arrow buttons, scroll to the "Read Codes" option then press the "Enter" button on the faceplate of the code reader.

Write the code number and the description of the displayed problem code(s) on a piece of paper to refer to if the MIL light is tripped again in the near future. This way, you'll be able to determine if the same problem is reoccurring and if so, this may indicate repairs will need to be performed to keep the MIL from continuing to come on.

Use the up and down arrow buttons on the code reader to move the cursor to the "Erase Code" option. It may ask you if you're sure you want to erase the code and press the "Enter" button.

Start the vehicle's engine and look at the dashboard to see if the MIL light is out. If so, the computer has been reset. The vehicle's computer will now run through a series of self-diagnostic resets called IM monitors. To allow it to do so, just drive it as you normally would and it may take a day or so to run through the self test. During this self-testing period the engine has to run to a certain temperature and then cool down and then maybe run again. If everything is OK, the MIL will remain out. If the computer detects a problem is still occurring, it will communicate that to the computer, which will re-trigger the MIL light. If that occurs, you should consider having the vehicle repaired.

Unplug the code reader when you're done, and shut off the car.


  • check Be sure the code reader you buy or borrow has an "Erase Code" mode. Some of the portable handheld code readers (especially in very inexpensive ones) only read the codes and do not erase them. You can also reset an engine computer by removing the negative terminal to the battery for 5 to 10 minutes, but this is not always recommended by certain models. It can temporarily create a poor-performing engine, and it may erase radio codes and all electrical memory devices like preset radio stations and clock settings.

Items you will need

About the Author

Jody L. Campbell spent over 15 years as both a manager and an under-car specialist in the automotive repair industry. Prior to that, he managed two different restaurants for over 15 years. Campbell began his professional writing career in 2004 with the publication of his first book.

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