A car diagnostics test costs anywhere from £30 to £100 in the UK, depending on the garage you take it to, and the make and model of your car. A diagnostics test can save you money in the long run, as it allows you to pick up on issues with your vehicle before they get worse and cause lasting damage.

You should book a car diagnostics test if you notice strange noises, vibrations, or smoke coming from your car, or if your engine warning light comes on.


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How Much Is A Car Diagnostics Test?

The price of a car diagnostics test depends on a variety of factors. It ranges from £30 to £100, depending on the garage, and the make and model of your car. Some newer models require more sophisticated equipment to carry out the test, therefore being more expensive.

A car diagnostics test may end up saving you hundreds or even thousands of pounds in repairs. The test will pick up minor issues that would develop into major problems if left undetected, saving you money in the long run.


What Is A Car Diagnostics Test?

A car diagnostics test is a test that reports on the condition of various parts of your car and their conditions. The test will include the engine, transmission, ignition coils, exhaust, fuel injectors, oil tank, airflow, coolants, throttle, and other systems.


How Does A Car Diagnostics Test Work?

Every car has an ECU – this stands for ‘Engine Control Unit’. This is where each of your engine’s sensors reports anything out of the ordinary. If there is a problem, the ECU will illuminate the appropriate light on your dashboard.

When the sensor detects a fault, a code is stored in the car’s computer system. When the mechanic plugs their diagnostics tool into your ECU, it will access the codes and the technician will know which part of your car needs repairing.

Once they have fixed the issue, they can clear the fault codes, and your ECU will revert to normal, and it will continue to scan for future issues.


What Are Car Diagnostic Codes?

The codes that your ECU deliver correspond to certain issues within your car. The codes follow a format of letters and numbers, the letter referring to certain areas of the vehicle:

  • B is for body codes. This covers aspects such as inside the passenger compartment, like the airbags, driver assistance, air conditioning, and passenger comfort and safety.
  • C is for chassis codes. This refers to the mechanical systems, such as the suspension, steering and braking.
  • U is for vehicle network codes. This includes the wiring and other integration systems like the sensors and computers.
  • P is for powertrain codes. This refers to the transmission and drivetrain parts, as well as the engine components.

Since there are over 200 fault codes, it is important that you take it to a qualified mechanic who will know what the code is for, and how to rectify the issue.


When Should You Get A Car Diagnostics Test?

There are several tell-tale signs that you need to have a diagnostic test. If you suspect there is an issue with your vehicle but you’re not sure what it is, a diagnostics test can tell you the problem, so you can fix the issue.


Engine Warning Light

If your engine warning light has been illuminated on your dashboard, a diagnostics test will tell you what has caused the light to come on. It looks like this:

An engine warning light as it appears on your car's dashboard.

Strange Noises

If your exhaust is abnormally loud, there is whining from your bonnet, brake squealing or gear crunching, a car diagnostics test can tell you what is causing these noises. The mechanic can then rectify the issues to get your car sounding as it should.



If the brake seems to be vibrating, you could need to look at your brake discs or pads. But it could also indicate an issue with your suspension or steering. A diagnostics test will clear this up.



This could signify that your engine is overheating, and you need to find out what is causing it.


How Long Do Car Diagnostics Tests Take?

The average car diagnostics test takes around 90 minutes to complete. It is usually the repair which takes longer – the mechanic will be able to walk you through this once they have discovered the issue.


Can I Do My Car Diagnostics Test Myself?

You can buy diagnostic tools from automotive shops or online. They range in price from as little as £25, but of course, the tool will not be as good as the one at a qualified garage.

If you are a confident amateur mechanic, a car diagnostic test should be fairly straightforward. However, if you are unsure, you should take your car to a garage to have a professional mechanic perform the test for you.

A mechanic will know the error codes and what is causing the issue.


Why Is A Car Diagnostic Test Important?

A diagnostic test is incredibly important to your safety and the functionality of your car. If your car is beginning to show any signs of deterioration, a diagnostic test can point you in the right direction to what needs to be fixed.

It can also pick up issues before they begin to damage your vehicle. If you can step in early enough, you could save yourself hundreds, if not thousands of pounds in repair costs.


Is The Diagnostics Test Included In The MOT?

Your diagnostics test is not included in an MOT. It can be beneficial to have your diagnostics test before your MOT so you can rectify any issues that are brought to light before your test, to increase your chances of a first-time pass.  


How Can I Save Money On My Diagnostics Test?

You can save money on your car’s diagnostic test by booking it through BookMyGarage. You can compare garages in your local area to find the best price. You can read reviews and filter by availability, rating, and location as price. Just enter your registration plate and postcode and start saving money alongside millions of other UK drivers.


Book online today!

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