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OBD Readers & Ports Explained

Jack Dreyer | Friday 25th November 2022 8:00am

Technician uses a tablet & OBD reader to perform diagnostic tests on a car.

If you’ve taken your car to a mechanic in the last 15 years or so, you’ve likely heard from them at some point that they’ve had to use the OBD port & reader to diagnose this or reset that – but what even are OBD ports & readers?

What is an OBD port?

A driver inspects an OBDii port located in the footwell of a car.

An OBD port is a port for an OBD reader. OBD stands for On-Board Diagnostics and the second generation, OBDii, is the most common standardised interface for car diagnostics in Europe & North America.

Think about it like USB: originally, every device had its own special port and you had to buy special cables that only worked with your particular device. But with the invention of USB, lots of devices can be connected without having to buy separate dongles for everything.

OBD was invented as a convenient way to program car computers and pick up masses of information from the various sensors.

What is an OBD reader?

OBD readers, as you may expect, exist to plug into the car’s OBD port and let you (or, more likely, the technician) know what’s going on behind the scenes. But they’re not just readers, they’re technically “writers” too – in the sense that you can manually change and reset things on the car’s computer where necessary.

Until quite recently, cars were complex mechanically, but electronically simple. That is, with enough patience and a small set of tools, almost anybody could take a car apart or make mechanical repairs. It was quite common, for example, for DIY enthusiasts to buy the maintenance schedule & repair guidebook of their particular car model and do any repairs themselves.

But with the growing complexity of cars, as well as the great shift to EVs, it’s become increasingly necessary to have specialist tools and advanced knowledge.

OBD readers are one element in the modern technician’s toolkit to help diagnose and repair numerous issues.

What kind of things can you read using OBD?

A technician uses an OBD reader to read information and conduct diagnostic tests of a car.

You can read a mind boggling amount of information from your car’s sensors, there are things like TPMS warnings & historic data, steering angle alignment, ABS condition, mileage, engine performance & injector coding, and even information on this like a diesel particulate filter.

Many cars, for example, will have a Service light that turns on after a certain mileage to remind you to take your car to a mechanic for regular checks & maintenance. This needs to be manually reset by a technician after a service has been performed.

Similarly, there’s a whole host of things that can be reset – but you can’t go resetting things yourself without actually fixing them. At least not if you want your car to keep functioning properly.

Can I do OBD resets myself?

Technically, you can buy relatively inexpensive OBD scanners & readers online and read basic diagnostic information – but you’ll be limited in what you can actually do with these. A professional grade OBD reader can cost hundreds of pounds. These are used by trained technicians so that nobody’s ever banging a wrench inside your car’s electronics (so to speak).

The cheap OBD readers are often cheap precisely because they don’t offer a great deal of functionality outside of basic diagnostic information (i.e. not much more than your Check Engine Light tells you) – and they often put greater functionality behind a paywall.

The detailed information that professional OBD readers can access is intended for professionals to accurately fix problems. If you’re having problems with your car, save yourself the hassle and bring it to your local Kwik Fit centre for expert diagnostics and repairs.


Any facts, figures and prices shown in our blog articles are correct at time of publication.




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