A guide to car diagnostic tools

Car diagnostic tools are necessary for fixing modern engines full of electronics. Parkers explains.

A car engine bay

by Chris Williams |

A diagnostic tool is self-explanatory in its function: it identifies car gremlins. However, before we go through the best ones, let’s answer some important questions.

What's the point of a car diagnostic tool?

Having a device that tells us what problems a car has is great, but if we aren’t mechanics who can act on the identified faults, surely it’s a bit pointless? Like a home-use Hubble Space Telescope diagnostic tool.

Not quite true.

Granted, basic car fettling has changed since high-tech electronics made their way into mainstream cars. However, that itself is exactly why car diagnostic tools are useful these days. Ever-more frequently do we take our cars to be serviced and have to fork out large amounts of money for faults that we don’t understand or have explained to us. With a diagnostic tool, we can send our cars to be serviced with a much better idea of what the fault is.

Use the information to undertake some internet research to make yourself informed about the issue, then take your car in to be serviced. In doing this, there's the potential to save yourself a considerable amount of money in servicing costs.

It's easy to give manufacturers and mechanics the benefit of the doubt with sorting your modern car’s faults without sliding in extra or unnecessary costs. However, diagnostic tools connect to a car’s OBD II port, which is quite often hidden in the car somewhere obscure. One could argue this is meant as a slight deterrent for people wishing to run car diagnostics at home.

There is a difference between readers and scanners

The most obvious difference between code readers and scan tools for cars is the price. Scanners are more expensive on the basis that they do more. Readers can essentially identify generic issues, whereas scanners are able to also read vehicle or manufacturer-specific codes.

We recommend readers for those who wish to understand a bit more about car troubleshooting and scanners for the more serious home mechanics and DIYers.

How do diagnostic tools work?

Fairly straightforward: turn your car off, and once you have located your car’s OBD II port (this may take some research), plug the diagnostic tool in. OBD II ports are often found beneath the steering column.

Turn the ignition to whichever setting the tool suggests. Your scanner or reader will then either power up automatically, or you’ll need to turn it on. Then follow the prompts and enter the required information - usually basic car details.

From there, you will be able to use the diagnostic tool to read trouble codes.

Obviously, individual tools will have certain limitations, and as mentioned, readers will only give you basic information – a trouble code it may identify could have various causes. This is where scanners step in.

Below is our pick of the best car diagnostic tools. Remember that you should check your car’s compatibility with any of them first.

The best car diagnostic tools


Editoru2019s pick

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This is a comprehensive little device packed with ability. It is extremely easy to use and will be able to test areas such as the fuel management system and the 02 sensor. Great for DIYers.

Autel AutoLink AL319 Reader

Best value reader
Autel AutoLink AL319 Reader

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A quality and highly-rated reader that will allow you to easily identify and clear error codes that might otherwise cost a fair bit to fix at the garage. In addition, it'll provide you with a basic understanding of what faults are plaguing your car when you take it in to be sorted by the professionals.

Launch CRP123X Scanner

Best value scanner
Launch CRP123X Scanner

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Dive into the world of car diagnoses with the Launch. Engine system, transmission, ABS, and SRS system diagnoses are all in this device's repertoire. An auto-VIN function makes for fast vehicle identification, and Wi-Fi makes for easy updates, report uploads and troubleshooting.

Autel MaxiCOM MK808 Scanner

Best scanner
Autel MaxiCOM MK808

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Autel is one of the big names in this arena and it's unlikely you'll need anything more than the Autel MK808. There are even more expensive units around but this is still in professional territory. It offers 25 service functions including oil reset, injector coding, throttle, and suspension. It comes with 12 months free updates.

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