How much does a car diagnostic test cost in the UK?
A car diagnostic test in the UK typically costs around £50 to £100 at an independent garage and £80 to £150 at a main dealer. The fee usually covers reading the fault codes and a basic assessment, and is rarely refunded against repairs, though some garages waive it if you have the work done.
What a diagnostic test is
A diagnostic test connects a scan tool to your car's OBD2 port, reads the fault codes stored by the engine and other systems, and interprets them alongside live sensor data. It is the starting point for finding a fault: it points to the area at fault, but it does not, by itself, carry out the repair.
Typical UK prices in 2026
Prices vary by location and how deep the investigation goes. As a rough guide:
| Where | Typical cost |
|---|---|
| Independent garage | £50 to £100 |
| Main dealer | £80 to £150+ |
| Fast-fit / quick code read | Sometimes free to £40 |
| One-off plug-in code reader (DIY) | £20 to £120 to buy |
A quick code read that simply pulls the stored codes is cheaper (and occasionally free, as a goodwill check) than a full diagnostic investigation, where a technician spends time tracing an intermittent or complex fault.
What the fee includes
- Reading and recording the stored fault codes.
- A basic assessment of what the codes point to.
- Usually a short report or verbal summary of the likely cause.
It does not normally include the repair, replacement parts, or deep component testing. Those are quoted separately once the fault area is known.
Do you still pay if they find nothing?
Usually, yes: you are paying for the technician's time and equipment, not a guaranteed answer. Many garages will, though, put the diagnostic fee towards the repair bill if you go ahead with the work. It's worth asking before you book.
How to avoid overpaying
- Ask whether the fee is waived or credited if you have the repair done there.
- Get the specific fault code and a written summary, so you can compare quotes.
- For a simple stored code, like a light after a loose fuel cap, a cheap plug-in reader can save a trip.
- Be wary of a quote to replace parts before the fault has actually been traced.
Frequently asked
How much does a car diagnostic test cost in the UK?
Typically £50 to £100 at an independent garage and £80 to £150 or more at a main dealer. A quick code read can be cheaper, and the fee rarely includes the repair.
Do garages charge just to read fault codes?
Often yes, though some offer a quick code read for free or a small fee as goodwill. A full diagnostic investigation, tracing an intermittent or complex fault, costs more because it takes a technician's time.
Is a diagnostic test worth it?
If a warning light is on or the car is misbehaving, yes: it points to the fault area and saves you replacing parts on guesswork. Ask whether the fee is credited against the repair.
Can I do a diagnostic test myself?
You can read stored fault codes yourself with a plug-in OBD2 code reader, which costs about the same as a single garage scan. MotoCore One is gaining built-in fault-code reading and clearing before its public release, so it will do that read on your dash too, alongside live data. Interpreting a complex or intermittent fault, though, is still where a garage earns its fee.