Amazon has announced a big sale on car diagnostic tools this week, but you'll need to be quick

You might be an enthusiastic and clued-up home mechanic, or you might, like me, be a bit of a Luddite when it comes to the oily bits in your car. Either way, it pays to invest in a good diagnostic tool.

These little gadgets were once the preserve of the professional, and to have one plugged in would cost an hour's labour in some garages, but anyone can now check in on their car's health any time they fancy with a fault code reader. They work by connecting to your car's internal computer through a dedicated port that all cars built this century should have, and they're designed to read out fault codes, which are stored every time the engine notices something's not right.

This could be a temporary glitch detected by a sensor, or something more serious that could lead to a major failure. Either way, if that "check engine" light comes up on your dashboard, it pays to have a diagnostic tool so you can have an idea of what might have triggered it. The codes these tools extract will be pretty meaningless to start with, but a quick internet search will reveal what they mean, and there are plenty of websites out there which can advise how serious the codes are.

In most non-severe cases, you can use the diagnostic tool to clear the code, drive the car for a bit, and see if it comes back, and if it does then it's time to get professional help. Or, if the code is suggesting there's a more serious issue, you'll know how urgently you need to get it looked into, and whether it's safe to drive the car at all.

Importantly, if you're in any doubt always seek professional help. These tools will not fix your car, they'll only help you identify a potential problem. But many garages charge upwards of £40 just to gather up your fault codes, so owning a diagnostic tool can be a great money saver.

Here are the devices Amazon is discounting this week, with the deals set to expire on Sunday, August 18.

1. Mucar Universal OBD II Code Reader

Was: £20.99, now: £16.33 - saving 22%

The cheapest device in the sale, the Mucar universal code reader is by no means a basic tool. It has a colour display to help you see live data and pick up any fault codes, and it looks really well made and sturdy.

Reviewers have generally been really happy with its functionality, value for money, and its ease of use. Some have said clearing codes can take a few attempts, but most have found it works fine.

2. Topdon AL300 OBD2 Scanner Code Reader

Was: £30.99, now: £23.24 - saving 25%

Another straight-forward unit with another decent saving, the Topdon Al300 also has a coloured screen, and plenty of functions beyond the basic code reading and clearing.

This one has even better reviews than the Mucar above, with a 4.2-star rating, and most customers enjoying its compact size and clear screen. This one looks like a great all-rounder for the money.

3. Xtool AD20 Pro Wireless OBD2 Scanner

Was: £64.99, now: £39.99 - saving 38%

A slightly different approach to the job, from this wireless scanner. This one connects to a smartphone through Bluetooth, and the information it collects is conveyed through an app. This will mean a better screen, and increased functionality, as well as having a search engine only a tab away for researching those codes.

In theory, with this device, you can leave it plugged in to the car's OBD2 port for constant monitoring, with the smart terminal app conveying live data from your engine. But it can also be used as a code reader just when you need it.

4. Mucar CS90 Car Diagnostic Tool

Was: £179.95, now: £123.55 - saving 38%

Getting closer to a professional-grade device now, there's a big saving on this much more complete diagnostic tool, which has its own built in file of potential code definitions, so you shouldn't have to go off to "Google".

This is perhaps a device more suited to home mechanics with a deeper knowledge and understanding, but its ability to provide printed reports of the condition of your engine will be handy for everyone, because it could save your mechanic time when you need to call in the cavalry.

A strong set of reviews on Amazon makes this a potentially great investment.