Bob's diagnostic bay handles same-day fault-code scans in most cases if you call before noon. Full scan reads all modules (engine, ABS, airbag, transmission, body control) and returns a plain-English report — cause, likely fix, honest £ estimate. Typical turnaround: 45–90 minutes. No dealer prices, no upsell.
What 'same-day diagnostic' actually means at an honest garage
In dealer marketing, 'diagnostic' means £150 flat fee, an hour of a technician plugging a Snap-on into your OBD port, and a two-line email saying 'P0420 detected, recommend catalytic converter replacement £1,850'. That's not diagnostic — that's code-reading with a markup. A proper same-day diagnostic at an independent means: read every fault across every module, review freeze-frame data captured when the fault triggered, check live sensor readings against known-good values for your engine, physically inspect the likely cause, and give you a written report saying what the fault actually is versus what the code says. On a P0420, that means testing whether the catalytic converter is genuinely failed or whether it's an upstream O2 sensor lying to the ECU. Different fault, different price — often £120 vs £1,850.
When same-day diagnostic is worth booking today (not next week)
Book same-day if any of the following is true: engine management light came on today with a noticeable change in how the car drives (loss of power, misfire, rough idle), you've got an MOT booked in the next 7 days and a warning light is showing, the car is due to be sold or part-exchanged this week, you're about to drive it long-distance, or a garage has quoted you £500+ for a repair and you want a second opinion before you commit. In those cases, an hour today saves you weeks of driving with a fault getting worse — or thousands of pounds on a wrong quote. If the light came on months ago and the car drives fine, next week is honestly fine.
What Bob's diagnostic report actually includes
Every same-day diagnostic at Bob's workshop leaves with a printed report: (1) every stored code across every module (not just the engine light), (2) freeze-frame data showing what the car was doing when each code was set, (3) live-data trace of the relevant sensors during a road test, (4) plain-English translation of what the code means for THIS engine, (5) recommended next step with an honest £ range, (6) whether it's safe to keep driving. If the answer is 'this car is fine, someone reset the light before you bought it', the report says that too — even though it means we don't get the repair. That report is yours to take to any garage; it's not locked to booking work with us. That's how an honest indy diagnostic looks.
How much a same-day diagnostic should cost in the UK
Fair UK indy pricing for a full multi-module diagnostic in 2026 is £60–£90 for a scan-and-report, £90–£150 if the scan is followed by an hour of live-data investigation on a specific fault. Main dealer usually charges £120–£180 for the equivalent, with less depth. Anyone charging under £30 is running a code-reader, not a diagnostic. Anyone charging over £200 without a specific complex fault (intermittent electrical, CAN-bus fault, coded module replacement) is dealer-pricing. Bob's flat-rate diagnostic starts at £75 and rolls into repair labour if you book the fix with us — so the diagnostic is effectively free if it becomes a job.
Same-day slots — how to actually get one
Bob keeps two diagnostic slots free every day for same-day bookings. The trick is phoning by 10am — later than that and the day is usually filled with the previous day's MOT-follow-up work. Turn up with the car, drop the keys, we'll aim to have the report ready by end-of-day (often within a couple of hours). If the fault is complex enough to need parts on order or specialist diagnostic dwell time (misfire trace, intermittent ABS fault), we'll be honest and rebook you — but you'll leave knowing exactly what the fault is and what the fix costs. No 'we'll get back to you' vagueness.
Frequently asked questions
Can I get a car diagnostic done today?
Usually yes, if you phone before 10am. Bob's workshop keeps two same-day diagnostic slots free every day. Full scan and written report typically ready within 60–90 minutes of drop-off.
How much does a same-day diagnostic cost?
£75 for a full multi-module scan and report at Bob's, waived against repair labour if you book the fix. Fair UK indy range is £60–£150 depending on depth. Main dealer £120–£180 for less thorough work.
What's the difference between a code read and a proper diagnostic?
A code read tells you which fault code is stored (£10 at Halfords for free). A diagnostic tests WHY the code triggered — often the code names one part but the actual cause is a sensor upstream. A proper diagnostic saves you replacing the wrong component.
Is a same-day diagnostic safe to trust for a big repair decision?
Yes, if the diagnostic includes live-data verification, not just code-reading. The written report should name specific tested values (fuel trims, O2 voltage, MAF g/s) and compare to known-good. Ask for that level of detail before you commit to any repair over £500.
Do I need to leave the car all day for a same-day diagnostic?
No. Drop the keys, we'll call you when the report's ready — usually 60–90 minutes. Complex intermittent faults may need to stay longer, but you'll know within the first hour.
Can Bob's diagnose faults on any make of car?
Yes. Diagnostic kit covers all major UK makes to manufacturer level, including VAG (VW/Audi/SEAT/Skoda), BMW, Mercedes, Ford, Vauxhall, Nissan, Toyota, Land Rover, Volvo, Peugeot, Citroen, Renault, Kia, Hyundai, Honda, Mazda and Suzuki. Coding limited on newer German cars — we'll flag that upfront.