What do we check for in a diagnostic check?

It’s unlikely that you have not come across the term ‘diagnostic check’ before, but do you know what it does and when it should be undertaken? If not, you are certainly not alone. This month’s article is here to explain all there is to know about it so that you can be sure your vehicle is running well, and you can catch problems before they turn into large, expensive repair or maintenance jobs.

What is a diagnostic test?

Gone are the old vehicles when a mechanic would lift the bonnet and start looking at each component to try to figure out what has gone wrong. Nowadays it’s a case of connecting the diagnostic computer to your engine’s ports and download key information about your engine and its performance.

What does it check?

A diagnostic test will check for problems with your engine, the exhaust system, the brakes, fuel injector, throttle, ignition coils, air flow and coolant.

While it can pick up that something is wrong, it will not be able to pinpoint the precise problem or reason – this is where your mechanic’s experience and expertise come into play. What it will do is identify the area where the problem lies and show the technician which parts are out of range so that they know where to start looking for the underlying cause. A far cry from the old days when all they had to go on was your description of a peculiar sound or feeling, or a warning light.

When should you get a diagnostic check?

Most people think that it’s something that will need to be done when a warning light appears on your dashboard. Diagnostic checks are useful on a precautionary basis as well as they will be able to detect anomalies before they become big enough to trigger that warning light. No one knows your vehicle better than you either; when you feel that something isn’t right – a new or different sound, a different feel to handling – a diagnostic check can pick up the problem before it turns into something bigger that could leave you stranded on the side of a motorway.

An annual diagnostic check is a good idea. You can ask your mechanic to do it at the same time as your annual servicing.

If you are buying a used car a diagnostic check is a very useful tool in determining the condition of the vehicle and its engine. Whether you are buying from a professional dealer or a private seller a mutual agreement for a diagnostic test will be money well spent. If they refuse, consider walking away from the deal.


A diagnostic check need not be expensive and doesn’t take long to run either. It can, however, save you a lot of money in the long run if it picks up an issue that can be tackled sooner rather than later, avoiding the potential escalation of a small problem into something much bigger that in the worst-case scenario could mean the need for replacement of expensive parts.

For a diagnostic test or for more information on what it does and how it can benefit your vehicle, talk to our skilled mechanics at Double Dee Autos. Simply give us a call on 020 8460 3040 with any questions or to book an appointment.