Book a Car Diagnostic in Cardiff

Trustpilot rating for all RAC Mobile Mechanics.

Why choose the RAC for a car diagnostic?

With RAC Mobile Mechanics, you can avoid the hassle of taking your vehicle to a garage. They can do a vehicle diagnostic check on your driveway, so you don't even need to leave the house.

When it comes to diagnosing issues with your vehicle, our friendly expert mechanics are here to help. We use state-of-the-art diagnostic equipment to accurately identify any problems, ensuring your vehicle runs smoothly and safely. The price includes the diagnostic service – no hidden costs. Just friendly, honest experts.

Close up of an RAC Mobile Mechanic underneath a car

Our top pick in Cardiff

We’ll come to you at home or work

RAC Mobile Mechanic in Cardiff

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At the RAC, we’ve got over 125 years’ experience in offering complete peace of mind® to our members. We’re best known for our breakdown service. And now – our new RAC Mobile Mechanics are here to help make every day motoring easier. If you need a service or repair, they’ll come to you at your home or work.

Close up of an RAC Mobile Mechanic running a vehicle diagnostic check

Book a car diagnostic

Our mobile mechanics will spend up to 30 minutes checking your car for faults and talk you through any repairs you might need and give you a report for your records. There are various ways we can check for faults, which could include plugging in to check your car’s onboard engine management system.

OEM quality parts

We use original equipment manufacturer (OEM) standard parts, which means every new part will be the same standard and same quality as the original part it replaced.

Mechanics you can trust

Our mobile mechanics are friendly, honest, and backed by the RAC.

Book a repair

It’s easy to book a car repair online. We bring the garage to you with RAC Mobile Mechanics, or find a trusted local garage. Common repair jobs include:

Clutch Replacement

We diagnose and repair clutch issues – whether your clutch is heavy or slipping, or you’re having trouble changing gears.

Alternator repair

We check and correct alternator faults to keep your charging system running smoothly.

Oil change

Oil is vital to a healthy engine, so it’s important to change it regularly.

Brake pads & Discs

If your brakes are making noise or you’re noticing reduced stopping power, it’s likely time to replace your brake pads or discs.

Average cost of a vehicle diagnostic by car make^

The RAC charges a flat rate for the cost of a car diagnostic but prices may change due to inflation. According to RAC data, the average cost of a car diagnostic is £87.

Make	Average price
Ford	£105
Vauxhall	£105
Volkswagen	£105
Peugeot	£104
Mercedes-Benz	£104
Nissan	£106
BMW	£107
Audi	£106
Renault	£104
Citroen	£104

^Average price quoted for RAC Mobile Mechanics from 01/01/25 to 31/03/25.

And it’s not just car diagnostics that we do in Cardiff

Mobile mechanics bring the garage to you, saving you the hassle of getting your car to a garage. If you need a service or repair, they’ll come to you at your home or work.

A close up of an RAC mobile mechanic looking under the hood of a car

Try one of our RAC Approved Garages

View all garages

IN'n'OUT Autocentres Cardiff

At IN’n’OUT Autocentres we offer fixed prices MOTs and Servicing for any make and model of car with no hidden extras. We are proud to be a ‘Which? Trusted Trader’ so we are really a garage you can trust. We also have a 5 Star Trustpilot reviews rating. We provide OEM parts and 12 months warranty on all parts and servicing. We only use premium Castrol oils in all servicing. Our services are all completed ‘while-u-wait’ so you have never have the inconvenience of losing your car for the day. You can watch your car as it is being worked on through the viewing window or sit back and relax in our clean and comfortable customer lounges with FREE Wi-Fi and coffee and read the latest magazines. Check out our latest reviews and BOOK NOW!!

499 Cowbridge Rd W, Cardiff, CF5 5TG

Fairwater Garages

We are a family business with over 40 years experience in the motor trade. We believe in a totally transparent service and we regularly welcome customers into our workshop to show them exactly the fault their vehicle has. It is very important to us that you understand, in the case of a repair, what has gone wrong and how we intend to fix it. If you stand still in this industry then you get left behind. That is why we have invested heavily in the specialist equipment and training now required to repair modern vehicles. We have, in the case of all the main manufacturers, the same diagnostic equipment used by them, giving us a true dealer level capability.

Norbury Road, Fairwater, CF5 3AT

Cardiff MOT Centre

Are you looking for a friendly, family-run independent garage dedicated to the drivers of Cardiff, then you’ve come to the right place. We have over forty years’ experience in the motoring industry and are committed to delivering quality repair work at the most affordable prices. We are proud to offer a wide range of dealership-standard services at much more affordable prices. So, if your vehicle needs an MOT test or service, a diagnostic test, tyre repairs or replacements, brake inspections or a general repair, book an appointment with Cardiff MOT & Service Centre today.

13 Ipswich Road, Cardiff, CF239AQ

Town Garage.

We are an established local independent garage and are proud to be members of Autofirst Network – a nationwide network of independent garages operating to the Network’s 6 core values of Capability, Consistency, Care, Clarity, Cost Effectiveness and Customer Focus. For your added peace of mind we are members of the Motor Ombudsman service which is approved by The Trading Standards Institute. We are a independent family run business established in 1976. We are proud members of CVTS & Good Garage Scheme. We are based at old Town Llantrisant. We have vast experience in most aspects of vehicle maintenance and repairs. We work on anything from a classic Ford Escort and Mini to modern vehicles and vans. We have 2 MOT bays. We have modern technology to be able to repair newest vehicle, reset service lights, diagnostics to traditional techniques that sometimes a old fashioned approach may be required. Whatever your needs we hope that Town Garage of Llantrisant will be able to sort.

Newbridge Road, Llantrisant, CF728EX

Roy Hart Motors Limited

Established in 1968 Roy Hart Motors Limited has always been a family-run garage which prides itself on a high standard of work, friendly customer service and approachable expert advice. We are an RAC-approved garage and are audited every year to ensure our standards remain in line with RAC standards. If you would like to book an appointment for your vehicle, please do not hesitate to get in touch with us on

Winterstoke Road, Weston Super Mare, BS233YS

Frequently asked questions on car diagnostics

How much does it cost to diagnose a car problem?

The cost you pay can vary depending on the type of car and how complicated the diagnostic test. Check with your mechanic for a quote.

Is a car diagnostic test worth it?

Yes, a diagnostic test may save you a lot of money. It finds issues early before they become costly repairs. It can also keep your vehicle running efficiently and safely.

Can I do a car diagnostic myself?

While you can buy a diagnostic tool, interpreting the results needs expertise. It’s best if you to have a professional mechanic perform the test.

How long does a car diagnostic test take?

Diagnostic tests take from 30 minutes to a few hours. This depends on what issues are being looked at.

What are common car diagnostic codes?

Common diagnostic trouble codes include:

P0300: Random/Multiple Cylinder Misfire Detected
P0420: Catalyst System Efficiency Below Threshold
P0171: System Too Lean (Bank 1)

These are general examples, so your car may have different codes. Always check with a mechanic so you get an accurate diagnosis.

Is a car diagnostic test necessary for a service?

Yes, they are. Regular diagnostics can help keep your car in good health. It makes sure that underlying issues are addressed quickly, so you can drive with peace of mind on the road.

Again, keep in mind that mechanics might have their own checklists. Chat with your mechanic to be sure that they address any specific issues you have.