Diagnostic fees and what they actually cover

Use the code as a starting point

Treat a stored fault code as a starting point, not proof that a particular part failed. Before authorising a repair from the code alone, ask what vehicle-specific data and test results connect the code or symptom to the proposed work.

Ask the garage to describe what its diagnostic charge covers — for example technician time, equipment use, access work or manufacturer information — because the agreed scope, not this page, defines what you are buying.

What to do

• Ask whether the proposed process may include checking the code and freeze-frame data, trying to reproduce the symptom, inspecting or testing the relevant system, and ruling out alternatives. Do not assume the whole list is needed or included for your vehicle.
• Ask how paid time will be recorded and which tasks are included; connecting a reader is not, by itself, a promise of a confirmed cause.
• Ask whether access work may be needed and whether it is inside the agreed charge before it is started.
• If a diagnosis is proposed from the code alone, ask what check could confirm it on your car before authorising a repair. Apply the same caution to advice from a garage, a forum or this site.
• These are OBDCode UK's suggested questions, not a prescribed diagnostic standard and not a promise that each listed check is possible or useful for your vehicle.

Settle the basis of the charge before work starts

Regulation 9 of the Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013 requires the trader, before the consumer is bound by an on-premises contract, to give or make available the information described in Schedule 1 in a clear and comprehensible manner, if that information is not already apparent from the context. Sources: ^[5]

That duty does not apply to a contract which involves a day-to-day transaction and is performed immediately at the time when the contract is entered into. Sources: ^[5]

Schedule 1 lists the total price of the service inclusive of taxes or, where the nature of the service is such that the price cannot reasonably be calculated in advance, the manner in which the price is to be calculated. Sources: ^[6]

Schedule 1 also lists, where applicable, the arrangements for payment and performance and the time by which the trader undertakes to perform the service, the trader's complaint handling policy, and the existence and conditions of after-sales services and commercial guarantees. Sources: ^[6]

Section 50(3) of the Consumer Rights Act 2015 treats information provided by the trader in accordance with regulation 9, 10 or 13 of those Regulations as included as a term of the contract, and section 50(4) says a change to that information, made before entering into the contract or later, is not effective unless expressly agreed between the consumer and the trader. Sources: ^[2]

the total price of the goods, services or digital content inclusive of taxes, or where the nature of the goods, services or digital content is such that the price cannot reasonably be calculated in advance, the manner in which the price is to be calculated

What to do

• Ask for the answers by email or text, whichever way you book. Regulation 9 covers the information list for a contract made on the trader's premises; the same Regulations set separate lists for contracts made away from the premises and at a distance, so do not spend your energy working out which one applies — get the basis in writing either way.
• Take the handoff checklist from the code page with you: the exact code and any companion codes, whether the warning light was steady or flashing, and what the car was doing when it appeared. Time a garage does not spend re-establishing that is time it can spend testing.
• Ask for the diagnostic authorisation and the repair authorisation to be two separate decisions, with the second one coming back to you.

Checklist

• Is the diagnostic charge a fixed price for the job, or an hourly labour rate?
• How much technician time does it include, and is that time booked in or open-ended?
• What happens when that time runs out — does the garage stop and call you before spending more?
• Does the figure include VAT?
• Does it cover road-testing, live-data logging or leaving a logger fitted, and stripping parts to reach a connector?
• Is the charge waived, reduced or credited against the bill if you have the repair done there? Get the condition, not just the promise.
• Do you get a written report, and is it yours to take to another garage?
• What is charged if the fault does not appear while they have the car?
• Who do you complain to if you are unhappy with the work?

What you were told is part of the contract

Section 50 of the Consumer Rights Act 2015 treats every contract to supply a service as including as a term anything said or written to the consumer, by or on behalf of the trader, about the trader or the service, if the consumer takes it into account when deciding to enter into the contract, or when making any decision about the service after entering into the contract. Sources: ^[2]

Anything taken into account in that way is subject to anything that qualified it and was said or written to the consumer by the trader on the same occasion, and to any change expressly agreed between the consumer and the trader, before entering into the contract or later. Sources: ^[2]

Section 50 signposts section 54 of the same Act for the consumer's rights if the trader is in breach of a term that section 50 requires to be treated as included in the contract. Sources: ^[2]

Every contract to supply a service is to be treated as including as a term of the contract anything that is said or written to the consumer, by or on behalf of the trader, about the trader or the service, if— (a) it is taken into account by the consumer when deciding to enter into the contract, or (b) it is taken into account by the consumer when making any decision about the service after entering into the contract.

What to do

• Note the second limb: what the garage tells you mid-job, on the call asking whether to carry on, is capable of counting too. That is the call worth confirming by text afterwards.
• Write down who said what and when, the same day. A dated note or a reply-all email beats a recollection three months later.
• If a figure comes with a spoken qualification — 'that's only a guide', 'if it's straightforward' — the qualification travels with it. Ask what turns the guide into a price.
• Keep the booking confirmation, texts, emails, the estimate and the invoice together from the first day, not from the day it goes wrong.

When the diagnosis does not find the fault

If the reported symptom does not appear during the visit, do not assume either that no useful checks were possible or that a firm answer was guaranteed. Ask which stored data, inspections or tests were available without reproducing it, which were actually carried out, and what event or extra authorised time would justify a further step.

What to do

• Ask for that record at handover, while the technician still remembers the car, rather than requesting it weeks later.
• Keep a well-documented exclusion list and offer it to another garage. It may help that garage plan its work, but the garage can decide what to rely on and may need to repeat tests; the record does not guarantee a cheaper or conclusive second diagnosis.
• If the light returns, log the date, mileage, weather, engine temperature and what the car was doing, then go back with that log.
• OBDCode UK's recommendation is to assess a no-result visit against the agreed scope and the record of work, not only whether the symptom appeared or a cause was confirmed.

Checklist

• The codes present when the car arrived — stored, pending and permanent — and the freeze-frame data.
• Whether the fault was present during the visit or could not be reproduced.
• Which tests were carried out and what the readings were, against the expected values.
• Which components and circuits have been ruled out, and on what evidence.
• What the technician recommends next, and what would need to happen for a firm diagnosis — the fault recurring, a longer road test, a logger left fitted.
• Whether the codes were cleared before the car was returned, and what to do if the light comes back.
• The date, mileage and the name of the person who did the work.

The contract backstops on skill, price and time

Section 49 of the Consumer Rights Act 2015 treats every contract to supply a service as including a term that the trader must perform the service with reasonable care and skill. Sources: ^[1]

Section 51 of the Consumer Rights Act 2015 supplies a reasonable-price term only where the consumer has not paid a price, the contract does not expressly fix a price or say how it is to be fixed, and nothing treated as included under section 50 fixes one either. Sources: ^[3]

Section 52 works the same way for timing: it supplies a reasonable-time term only where neither the contract nor the information treated as included under section 50 fixes the time for the service to be performed. Sources: ^[4]

What those sections say in full, and the order of remedies that follows when a repair goes wrong, are set out on our guide at Your rights after a car repair goes wrong. This page does not repeat them.

What to do

• Do not treat the reasonable-price rule as a plan. It is a backstop for the case where nothing was agreed, and what counts as reasonable is decided on the facts, after the argument has already started.
• The stronger position is the ordinary one: a price or a stated basis for calculating it, agreed before the keys change hands.

Fitting parts to see what happens

Where a garage proposes fitting a likely part to see whether the symptom changes, treat that as a proposed trial rather than a guaranteed fix. Before agreeing, keep three questions separate: what trial you authorise and at what price; whether the work stays within that authorisation; and whether the service is performed with reasonable care and skill.

What to do

• Ask whether the part is proposed because a test indicated it, or as a trial to see whether the symptom changes. If it is a trial, agree its price, limit and next decision before authorising it.
• Ask what result would confirm the proposed cause and what check has been done. If the garage says the component can be tested in place, ask for that option and its price before deciding.
• Set an approval limit and ask to be contacted before anything beyond the agreed diagnosis is fitted, so the substitution decision comes back to you rather than appearing on the invoice.
• Ask, before you agree, how the garage will charge if a trial part does not identify the cause, including the labour and whether the part will remain fitted. Get the answer in writing; this page cannot promise either payment or refund.
• Authorised but no result: if you agreed a bounded diagnostic step or trial replacement and it did not identify or fix the cause, compare the record and invoice with the agreed scope. Do not infer from the outcome alone either an automatic refund or that the agreed work was completed.
• Not authorised: if you say a part or task was outside your authority, ask the garage to identify when, how and at what price it says you agreed. Keep that scope dispute separate from whether the part fixed the fault.
• Reasonable care and skill concern: identify the acts, omissions and evidence that make you question how the service was performed, rather than treating the lack of a result alone as proof. Section 49's service standard is summarised above; the separate rights guide explains possible remedies without promising one.
• If a part has been fitted and made no difference, ask in writing what led to it and what will be done differently next, before agreeing to a second attempt.
• How estimates and quotes work, and how to handle authorisation for extra work once the car is stripped, is covered separately in our guide at Estimates, quotes and extra work: authorising a garage repair.

Important

OBDCode UK does not publish diagnostic prices, hourly rates or typical ranges, and does not track what garages charge. This page therefore offers no verified UK market range; ask for a written price or calculation basis specific to the vehicle and the agreed scope.

Do not drive a vehicle that the reviewed safety conclusion tells you to stop driving in order to reach a cheaper garage. Arrange recovery instead.

OBDCode UK does not recommend, rank or receive commission from any garage, and is not paid for any repair or diagnosis you book.