Car diagnosis tools

How to Use a Car Diagnostic Tool

Nidhi Nangia
By Nidhi Nangia. Updated: September 5, 2019
How to Use a Car Diagnostic Tool

Today’s modern cars are a great mix of mechanics as well as technology. Most cars come with automated features that help you stay safe and convenient while driving. Many of them have their lights turned on whenever there is a problem with your car’s engine or performance. But sometimes, these lights can be a bit of a nuisance. The ‘check engine’ light may turn on suddenly while driving, and you have no idea what the hell to check in your car’s engine. You are not a professional, and you don’t know what kind of fault your car’s engine has come up with. In that case, a car diagnostic tool comes to your rescue. This is a little device that helps you pinpoint the error that your car is having at present. You have to connect this device to your car, and locate the exact point of trouble within seconds. Read this oneHOWTO article to find out how to use a car diagnostic tool.

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  1. Choose your car diagnostic tool
  2. Locate the iagnostic Link Connector (DLC)
  3. Look for problems
  4. Car make and model
  5. Choose your code
  6. Code list
  7. Check the alphabet
  8. Crack the code
  9. Reset

Choose your car diagnostic tool

If your car is built before 1996, you will need an OBD-1 scanner, but if it is newer than that, you need an OBD-II car diagnostic tool. Since this article is written in 2017, we will go with the newer model. The tool will constantly monitor your engine’s performance, along with its emissions control system. The check engine light will turn on whenever there is malfunction in your car.

How to Use a Car Diagnostic Tool - Choose your car diagnostic tool

Locate the iagnostic Link Connector (DLC)

If there is some problem in your car and the check engine light has turned on, the first thing you need to do is to locate the DLC in your car. This Diagnostic Link Connector (DLC) is a triangular 16-pin connector that you will commonly find below the dash on the left hand side, probably near your steering column. If you cannot locate it, refer to your car owner’s manual and find out where it is.

Look for problems

Once you have located your DLC, insert the car diagnostic tool connector into it. Turn on the ignition of your car without starting the engine. When you do this, the tool will start communicating with the automated systems of your car. Keep looking for the messages that appear on the tool’s screen, such as ‘searching’ or ‘establishing link’ etc. If your screen is blank, try to jiggle the connector to make a better connection between the DLC and the diagnostic tool. The older your car, the poorer connection it will show.

Car make and model

Some car diagnostic tools will require you to enter your car’s make and model details, along with its VIN (Vehicle identification number, which you'll find in your insurance documents, registration card or vehicle title) and other codes, including your engine type. Different tools may have different requirements that you have to enter.

Choose your code

Once you have entered your car’s details, the tool will boot up and you have to select ‘codes’ to open up the codes menu. You will see a few systems like powertrain, airbag, transmission, brakes etc on the screen. Pick one and see the types of codes appearing now. An active code is a live code or malfunction that keeps your ‘check lights’ on. A pending code appears when the car diagnostic tool has failed the operations of your ECU system.

How to Use a Car Diagnostic Tool - Choose your code

Code list

Each code starts with a letter that refers to the system that the code wants to designate:

  • P stands for powertrain, which includes your engine, fuel system, transmission, emissions, ignition and others
  • B stands for body, which includes your power seating, seat belts, air bags etc.
  • C stands for chassis, which includes your axles, brake fluid, ABS etc.
  • U stands for undefined, that covers the rest of the aspects of your car.

Check the alphabet

The alphabets are followed by certain numbers, and the last two digits refer to the specific issue that needs to be addressed. For instance, P0301 refers to a misfiring condition in the first cylinder. It may indicate a worn out plug wire, spark plug or vacuum leak near the number one cylinder.

Crack the code

Understanding the codes takes several years of practice and experience. Once you have identified the code, tell it to your auto repair professional and he will be able to resolve it within minutes. However, your car diagnosis tool should come with an instructions brochure where you can find the meaning of the code so you can identify the problem.


Don’t forget to reset the check engine light using the main menu of your car diagnostic tool. Otherwise, it will stay on and catch your attention every now and then.

To do so, make sure you press "erase" or "clear" on the error code. This should turn off the engine light in your car.

if you have already disconnected the car diagnostic tool, you can also do so by disconnecting the car battery's positive and negative cables and wait for 30 minutes before you reconnect your car's battery once again.

How to Use a Car Diagnostic Tool - Reset

If you want to read similar articles to How to Use a Car Diagnostic Tool, we recommend you visit our Car Maintenance and Repair category.

Write a comment
What did you think of this article?
Jack Hodges
Is article was great it was very helpful I'm going to come back and once I diagnose what is wrong I'm going to come back and see what it means and I think this is great
OneHowTo Editor
Let us know how it goes Jack!
tuyishime vedaste
so interresting
Kenneth Hance
very well explain
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How to Use a Car Diagnostic Tool