Car diagnostic tools may seem like they’re for workshop technicians and repair specialists. But what if we told you that for not a lot of cash, you could invest in a pocket-sized device for yourself and use it at home? It’s an unusual car tool, but one that could really save you cash when something goes wrong with your vehicle.
That’s the beauty of modern car diagnostic tools; many of them are Bluetooth enabled, so you can pair them up to an app on your phone and browse the faults on your vehicle from there. These little fault-finders are designed to make car maintenance less daunting and less expensive for the potential consumer.
When you take your vehicle to a garage to diagnose and fix a fault, you can be forking out hundreds – and potentially thousands – of pounds for hourly labour rates for technicians to open up their toolkits and find where the fault is, order the parts to fix it, and additional hours of fitting them. It can easily prolong if the fault isn’t immediately known, and this can get expensive. The problems don’t quite end there, either.
Data from car diagnostic tools specialist, Carly, reveals that 77% of women don’t fully trust car garages to be fair and honest with them. And 50% believe they have been mis-sold and/or lied to about the actual state of the vehicle and requirements for repairs. Additionally, 55% of women feel they need to be accompanied by a man when taking a vehicle to a garage to be taken seriously and treated fairly.
This is concerning stuff, and given that motoring is both expensive and a necessity for many people, being treated with honesty and fairness should be the top priority of all parties involved. So, how can we as individuals tackle this? One of the answers is keeping a little scanner handy.
So, where do car diagnostic tools come in?
Granted, basic car fettling has changed since high-tech electronics made their way into mainstream cars. There’s considerably more to it than just engine oil and filter changes nowadays. However, that is exactly why car diagnostic tools are useful these days.
Ever-more frequently do we take our modern 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 repaired with a much better idea of what the fault is. That way, users can ensure they know what needs repairing and potentially save hundreds, if not thousands of pounds on parts and garage labour.
How we tested car diagnostic tools
We gathered each of the car diagnostic tools that was provided and plugged it into a compatible vehicle. Generally speaking, these are cars with an OBD2 port that were manufactured from 2001-onwards. Alongside the individual apps for each scanner, we then used the data to assist us on how diagnosing a fault. We also factored in whether the extra features were any good, they often extended to far more than just the fault pages, with some including a whole vehicle database.
Meet the experts
Aaron Hussain
Commercial Content Writer and products tester, Aaron has been writing for Parkers since 2023 after acquiring his masters degree in Automotive Journalism from Coventry University. His enthusiasm for cars stretches back to before he could walk, and the passion for looking after them shows no bounds as he daily drives a classic Mercedes-Benz, rain or shine.
His role at Parkers is simple: to advise people on the best methods and equipment to make their motoring life hassle-free. Whether it’s a jump starter pack that can get you moving again or a phone mount to keep your Google Maps in check, Aaron recommends the most useful products to enhance car life.
The best car diagnostic tools
The best car diagnostic scanner
It even integrates a Cost Repair Calculator, which gives you a rough idea of how much a scanned fault is going to cost you. The cost and subscription of the device differs between car brands, so with Mercedes-Benz, you're looking at a £53 starting price for the scanner.
How well does it work then? The simple answer is rather excellently, but not without a few glitches. Sometimes, the we've found the app close itself when opening, and other times, a rating pop-up appeared seemingly every 30-seconds. These were rather annoying teething issues that in recent times, haven't appeared.
Onto the good bits: it's super-easy to connect to your phone and vehicle. You just have to wait a while for the device to read the vehicle in question and read its faults. We tried it on a 2020 Seat Leon Cupra, various BMWs, and Volvo V60, and the device took a good 5-10 minutes to read each car. You can expect it to take longer on a larger, more techy car like a Audi A8, and less on a bare-bones Dacia Duster.
I was greatly impressed by how thorough the fault codes were - and inputting the information onto the Repair Cost Calculator resulted in some pretty comprehensive theories. I've even used it myself to view a used car recently, and had to walk away due to the device picking up some pretty alarming codes that weren't mentioned in the ad. Despite its flaws, I'm smitten by the Carly scanner and like all the features that comes with it.
My personal favourite is the Free Used Car Check - available in the app once downloaded. Again, it had some teething issues, but these have since been ironed out since its introduction in 2024. I've used it for myself a few times when checking out second-hand cars for sale.
Review by Aaron Hussain
Pros
- Easy to use and set up in any vehicle we've come across
- Includes a free used car check in the app, which is a neat bonus
- Provides fairly accurate data, including estimated repair costs (take these with a pinch of salt, mind)
Cons
- Reading a larger vehicle, such as a Range Rover, will take some time
- The app has been quite fussy and glitchy in our experience
| Vehicle compatibility | Universal |
| Type | Bluetooth/app |
| Dimensions | 7.7 x 4.5 x 2.3cm |
| Weight | 50g |
The best diagnostic tool for BMW and VW products
Rrp: $103.80
Rrp: $103.80
It's a little smaller than the Carly scanner, but how well does it work? I plugged it into a brand new 2025 Audi A6 Saloon (C9) to see if a car that's merely months old could throw up some issues.
My report of the OBDeleven consists of mainly positives: it was a quick and easy thing to read the car and it was a lot quicker than the Carly device. Given that it's trained to read only certain brands, I should imagine it's engineered to quickly scan an Audi's electronic maze with ease.
One slight hiccup was making it recognise the new A6. It didn't initially do so at first, so I had to select the vehicle make and model before typing in the VIN number. Only after then, did it manage to scan the vehicle. It showed zero faults to report, though I'm reliably informed by my colleague that the rear seat sensor is being a little sensitive.
I like how compact the device is and the fact it has its own keyring. Whilst its quick and very easy to use with an intuitive app, it didn't recognise a fault known by the Parkers staff, so my trust for it isn't 100%.
Review by Aaron Hussain
Pros
- Very quick and easy to set up and has an intuitive app
- Reads a car very quickly, which is excellent for most people
- Compact device that can be carried around with your keys
Cons
- It failed to pick up a rear seat sensor issue on our test vehicle
| Vehicle compatibility | BMW & Volkswagen Groups |
| Type | Bluetooth/app |
| Dimensions | 4 x 2 x 4cm |
| Weight | 60g |
The best quality OBD2 scanner
As per the other scanners, it helps narrow down potential issues from electric window bugs to things deep within the bowels of the vehicle. It's compatible with most vehicles from over 60 brands produced after 2002, and you can check the compatibility with your vehicle using the brand's vehicle model table query function. This can be accessed on Topdon's website on the diagnostics page.
It represents pretty good value for money, too. Along with your £70 worth of scanner is a brand that is renowned for its battery charger range, so the quality and knowledge from its technicians is something to feel reassured about.
Pros
- Works very universally, meaning it caters for a wide range of vehicles
- Good value for money, considering the functions on offer and the good build quality
- Includes repair guides within the app, making things more straightforward for users
Cons
- Isn't quite as comprehensive as some others on the market
| Vehicle compatibility | Universal |
| Type | Bluetooth/app |
| Dimensions | 14 x 5 x 18cm |
| Weight | 100g |
The most versatile OBD2 scanner
It has over 26 different functions which include some very clever tweaks. Injector coding, airbag reset, suspension calibration, and headlight adjustment to name a few. It's catered for almost any vehicle on the market, so whether you have a Ford or a Porsche, chances are it'll slot in and analyse the inner bones.
It's also customisable in 23 different languages, which adds a lot of extra versatility points.
Pros
- Available in 23 different languages, which is great if you speak a number of them
- 26 different functions available, albeit they may be limited in usefulness
- Comptaible with over 150 vehicle brands, making it very versatile
Cons
- Doesn't represent as good value as the other options, stretching above £200
| Vehicle compatibility | Universal |
| Type | Wireless |
| Dimensions | 12.3 x 9.2 x 3.7cm |
| Weight | 100g |
The best value OBD2 scanner
The service features include tyre pressure monitoring reset, oil reset, throttle adaption and even airbag settings. It's a comprehensive bit of kit for such a small device and you can access a plethora of vehicle data just from one scan.
It's also relatively good value for money. At just under £70, it's comparable to the Carly, Topdon, and OBDeleven units and offers a lot of features for the price point. Bluetooth scanners isn't Autel's primary forte, but this certainly puts up a good fight against the competition.
Pros
- Good value for money compared to others at around £70 for the unit
- Is quite universal to a wide range of vehicles manufactured between 1996-2018
- Automatically recognises previous vehicles it was plugged into
Cons
- The service features are probably a bit gimmicky for most users
| Vehicle compatibility | Universal |
| Type | Bluetooth/app |
| Dimensions | 5.9 x 2.5 x 4.9cm |
| Weight | 35g |
FAQs
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How to use a car diagnostic tool
Quite simply, 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. -
What is the 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.
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. -
Are car diagnostic tools universal?
Some OBD2 scanners are designed to pair with a wide range of makes and models, whereas others are focused around certain brand groups. For instance, OBDeleven's device we tested only works with BMW and VW group vehicles, whereas others can cater for up to 150+ different brands.
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Are car diagnostic tools any good?
Quite simply, they are very good for picking up fault codes throughout different areas of a car. A modern car has many different modules and diagnostic scanners read through each and every one of them.
Where they're not so useful is uncleared codes. When reading a vehicle, scanners can sometimes pick up fault codes that haven't been cleared or have already been sorted - which can throw off the user. So, it's a good idea to keep a log of what has and hasn't been sorted if this happens to you. -
Are car diagnostic tools accurate?
It's a bit of a hit and miss, depending on the device. Most of the time, these scanners should have no issues picking up fault codes as they read hundreds of different modules and electronics throughout the vehicle.
But cheaper devices with little-to-no brand value or reputation can be inaccurate. That's why with this kind of product, it really is worth spending the extra cash on something more reputable. In our experience however, the diagnostic tools we've tested are accurate and point us towards faults within the vehicle, little or large.
It's also important to remember that while a lot of these little tools are accurate, they don't perform a full diagnosis on the vehicle. You kind-of have to treat them as pointers before you dig deeper and detect the actual issue.
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