Last updated: July 2026 — every price on this page was checked against the named UK sources on 8 July 2026.
A car diagnostic test costs £50–£100 in the UK — the band corroborated across ClickMechanic (£50–£101, average £65), FixMyCar (£51.66–£57.21 averages) and the RAC (£87 average; £99 flat fee for its mobile service), with Halfords from £49.99 (2026 prices).
It takes 30–90 minutes and reads the fault codes your car has already logged — the cheapest step before any big repair decision.
Diagnostic test prices compared
| Provider / source | Published price |
|---|---|
| ClickMechanic | £50–£101 by region (average £65), includes 0.9 hours labour |
| FixMyCar (marketplace averages) | £51.66–£57.21 |
| RAC (mobile mechanics) | £87 average; £99 flat fee |
| Halfords | from £49.99 |
| BookMyGarage (12-month booking data) | £66 average (£20–£159 full range) |
A transparency note: FixMyCar publishes two different averages on different pages (£51.66 and £57.21) — both are shown as printed. Model-level examples from its data: Nissan Qashqai £60.48, VW Golf £60.45, Ford Focus £56.37. Big-city bookings run higher: the RAC lists London at £104 and Bristol at £108.
What a diagnostic test actually includes
A technician plugs an ECU reader into the car’s OBD port to pull stored fault codes, test components and view live data (FixMyCar) — covering the engine, transmission, brakes, exhaust, ignition and fuel systems. The RAC’s version takes up to 90 minutes and ends with codes cleared after fixes and a report for your records; ClickMechanic’s includes 0.9 hours of labour, within which minor fixes are attempted on the spot. What it is not: a guarantee of the repair price — it names the fault, and the fix is quoted separately.
“Free” diagnostics: read the small print
FixMyCar says it plainly: free diagnostic offers are usually caveated, with the scan’s cost “baked into” the repair that follows. Genuinely free checks do exist — Halfords’ free 5-point and 10-point health checks cover lights, wipers, battery, tyres, oil and fluid levels — but those are visual once-overs, not an ECU fault-code read. No source we checked publishes a “fee deducted if you book the repair” policy, so if a garage offers that, get it in writing.
What affects the price?
- Where you live — £50 to £101 by region on ClickMechanic; £53 to £78 by town on BookMyGarage.
- Garage vs mobile — the RAC’s come-to-you service carries a £99 flat fee against ~£50–£65 at a garage.
- Make — premium badges nudge higher: BMW £58.30, MINI £60.40 on FixMyCar’s tables.
- What happens next — the test is the cheap part; its value is stopping you paying for the wrong repair.
Frequently asked questions
How long does a diagnostic test take?
Around 30 minutes at a garage per FixMyCar, under an hour on ClickMechanic and up to 90 minutes for the RAC’s fuller mobile check.
Is a diagnostic test worth it before a big repair?
Almost always — £50–£100 to name the actual fault is cheap insurance against a misdiagnosed clutch, gearbox or head gasket job costing hundreds. Our repair-or-scrap guides all start from a proper diagnosis.
Will the test tell me exactly what to fix?
It reads the fault codes the car logged and points to the failing system; interpreting codes still takes a competent technician, and some faults need further physical inspection beyond the scan.
Can I just use a cheap OBD reader myself?
Home OBD readers can show basic engine codes and are useful for a first look — but garages’ tools read more systems, test components live and clear codes properly after repairs. For a warning light that keeps returning, book the full test.
Related guides
Sources: ClickMechanic diagnostic inspection, FixMyCar car diagnostics, the RAC, Halfords and BookMyGarage, all checked 8 July 2026. See how we verify prices.