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How to Know When to Repair or Replace: Leveraging Car Diagnostic Tool

How to Know When to Repair or Replace: Leveraging Car Diagnostic Tool

Having car problems? Every trip to the mechanic demands a difficult decision - it is worth repairing or should you just replace it. Our friend, Tim Setterfield is here to show you how that decision is not as scary as you thought. Tim is an automotive writer and has written on a wide range of automotive topics. His inspiration stems from working with his dad when he was a kid in his garage.


Whether it’s fresh out of the showroom or a well-seasoned classic, your car isn’t going to last forever. The average lifespan of a car is getting longer thanks to robust manufacturing and increasingly reliable parts, but keeping your car in good working order takes vigilance during day-to-day use, and a familiarity with the signs that you need to repair or replace integral parts.

Though there are obvious signs that your car needs some attention; the engine light, poor mileage, bald tires and so on, sometimes you need to dig a little deeper. Your car may have a more insidious maintenance issue that’s being ignored simply because it’s not ringing the usual alarm bells.

If you love keeping your car in perfect working order and you feel like your intuition might be letting you down, this post is for you. Here’s a short guide to leveraging a car diagnostic tool to know when something needs to be repaired or replaced.

What You'll Need

Obviously, the first thing you’ll need is an OBD-II scanner. There is a wide range of scanners on the market with varying degrees of response speed, on-screen detail, and extra features such as printer connectivity. If you’re using it for private repairs, the model you choose just depends on personal preference, and how many of these features you’re planning to use. Do a little research into what’s available and you’ll quickly find the best OB2 scanner for your needs.

Generally, your vehicle will have to be 25 years old or younger to be compatible with an OBD2 scanner. While onboard computers have been around since 1968 in some form or another, they only became a universal feature in 1996, when the OBD-II specification became mandatory for all cars sold in the US.

Getting Started

Though a lot of people see diagnostic scanners as some kind of daunting, specialist tool, their basic operation is actually pretty easy. All you need to do is plug it in, and turn everything on.

The first step is locating your car’s OBD-II port. This is usually somewhere near the root of the steering wheel, tucked underneath the dashboard. If you can’t find it here, some models have it underneath the passenger-side dashboard, or somewhere on the center console. If all else fails, check your car’s user manual or look it up online.

Next, plug in your OBD-II scanner and start up the car. Though cars that store diagnostic codes on their onboard memory don’t need to be started up all the way, the engine will need to be running for you to see its checks in real-time.

Recording the Car Codes

Diagnostic tools work by receiving codes from the car’s onboard computer, each of them representing a specific maintenance issue. Though you’ll start to recognize some of the more common codes with experience, the raw code feed will look like gibberish to you the first time you use it. We’ll talk about interpreting them more in a minute.

Many OBD2 scanners will automatically start reading the codes as soon as you turn them on. You may need to punch in your car’s VIN number if using it for the first time or press a “scan” button to start the process manually.

The scan will run in a few seconds and display any specific error codes it finds. Many modern scanners will store these reads on their own memory, feeding them straight into diagnostic software or mobile apps that will interpret the raw codes into a description of the actual problems. If you’re using an older model, however, you may need to take note of the error codes that the scan comes up with, and manually research what they mean.

Note: Some devices will also have a “clear” option which will manually clear the codes and turn off your check engine light if possible. This will only postpone the next time the light comes on due to some unaddressed issue under the hood, but if you want to turn it off manually for whatever reason, then there might be a way.

Interpreting the Data

A lot of modern OBD2 scanners have built-in software that will turn the car’s raw data into plain English, giving you a code description that will help inform you of any repairs and replacements. However, if all your device is giving you is the raw codes, there are a couple of methods you can use to interpret it:

The first option is to research the error code online. A simple google search of the car’s error code will usually help you find the code description on the manufacturer’s site or automotive wikis.

The other option is finding a software suite that can interpret the codes for you. There’s a range of third-party software which will download the error codes directly from your OBD2 scanner, and interpret them into code descriptions.

Repairs and Replacements

Now that you’ve run your diagnostics and got the error code descriptions, you should have a good starting point to carry out the repairs and replacements your car needs.

Though you may be pretty experienced in DIY car repairs, there are a couple of things to bear in mind:

  • The error codes identified by your OBD-II scanner won’t always identify the car part that needs to be fixed or replaced. Sometimes an error that crops up in one car part will just be the symptom of a separate, more pervasive problem.
  • It’s possible that a scan from your diagnostic tool will miss the source of the issue entirely. If you’ve cleared the codes and you’re still experiencing problems, take your vehicle to a professional mechanic. They’ll have diagnostic tools that will be able to examine more systems and draw more detailed information than OBD2 scanners designed for home use.

A Word from BlackboxMyCar

Thank you Tim, for sharing such valuable information with us and our readers. Identifying certain problems with your car isn’t always the easiest thing to do. For those who prefer a more hands-on approach, you might need more than the ThinkOBD 100 or any basic OBD-II diagnostics tool. Got tips you want to share with the BlackboxMyCar community?
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