Guides for UK drivers

Last reviewed · OBDCode UK editorial

Every guide here is written the same way: whether the car is safe to drive comes first, then what you can check without dismantling anything, then what the job should cost in the UK and what to ask the garage. Figures come from DVSA open data or a named UK source with the date we read it.

How do you start when you have a symptom and no fault code?

Start from what the car is doing, not from a part you suspect. Each symptom guide opens with a drive-or-stop answer, then the observations you can make safely, then what to hand the garage. You do not need a code reader for any of it. A symptom guide will not name the failed part, and neither will a fault code.

Used 2020 BMW Pre-Purchase OBD2 Scan: Stored, Pending and BMW-Specific FaultsA generic OBD2 reader can retrieve emissions-related stored, pending and permanent codes. A BMW-capable tool may reach more modules. Neither scan proves the car is healthy on its own; treat it as one part of a pre-purchase check and do not clear codes for a seller. Four-System vs All-System OBD2 Scanners: What to Compare Before You BuyIf the jobs you actually do are engine, gearbox, ABS and airbags, a four-system scanner is enough. Pay for all-system only when the maker’s coverage list, the live tests and the update terms for your cars make the extra money worthwhile. A long feature list is not proof it will finish a named reset on your car. Engine management light on: steady or flashing?A steady engine management light means the computer has stored a fault. Drive with caution and get the code read. A flashing light is different — stop when it is safe. Do not clear codes to hide the lamp before an MOT. Flashing engine management light and juddering: stop and recoverNo — do not continue the journey. A flashing engine management light with the car juddering is a stop-driving situation: ease off only enough to reach the nearest place of relat… Car overheating but coolant looks full: stop and recoverNo — do not continue driving while the engine is overheating, even if the expansion bottle looks full. Move only far enough to reach a place of relative safety, switch off, and… Car won’t start and just clicks: what to do nowNo — while the car only clicks, it cannot be driven. Keep it parked, switch the ignition off and stop repeated attempts. Rapid clicks often mean the 12-volt supply is collapsing… Car turns over but won’t start: safe checks before recoveryNo — while the engine turns but will not start, the car cannot be driven. Stay parked, switch the ignition off and stop repeated attempts. Check only for fuel smell or leakage,… White, blue or black exhaust smoke: drive or stop?Drive only when a thin white vapour appears on a cold start and clears fully as the exhaust warms, with no warning light, rough running, fluid loss or fumes in the cabin. If whi… DPF light still on after driving: stop repeating the runCan I drive? No—not for another clearing run. If the DPF light stayed on after the handbook journey, park and arrange diagnosis. A red or flashing warning, power loss, smoke or… Brake pedal spongy or going to the floor: do not driveNo — do not drive, even a short distance to a garage. A newly spongy pedal, a pedal that sinks, or one that reaches the floor can mean braking pressure is not being maintained.… Battery warning light on while driving: stop safely and recoverNo — if the battery-shaped warning light stays on after the engine starts, comes on while the engine is running, or remains on while a hybrid or electric car is in READY mode, d… Car in limp mode: can you keep driving?Can I drive? Only for the shortest, gentle trip to a nearby garage, and only if the car can maintain a safe speed, no warning is red or flashing, temperature is normal, and ther… Failed an MOT: what to do before driving awayDo not drive away until you have read every defect and checked when your current MOT expires. A dangerous defect means the vehicle must not be driven until repaired: arrange rep… Noise from under the car: scrape, clunk, rattle or hiss?Do not keep driving if anything is hanging or scraping continuously, you smell or see fuel, exhaust fumes enter the cabin, or steering, braking or a wheel feels different — stop… Car cuts out when slowing down: safe next stepsRecord when the stall happens and treat any loss of control assistance as a recovery fault. Coolant keeps disappearing with no visible leakA falling cold level still means coolant is escaping; never open a hot pressurised system. Exhaust smell inside the car: stop exposureCabin fumes can expose occupants to carbon monoxide; smell strength is not a safety test. Car clunking over bumps: safe observationsA knock can come from cargo, exhaust or running gear; do not diagnose it by going under a jacked car. Car juddering or shaking: decide when to stopWhen the shake occurs is useful evidence, but flashing warnings, tyre damage or brake effects mean stop. Car loses power when accelerating: safe next stepsReduced power is a symptom, not a parts diagnosis; leave fast traffic and preserve warning and code evidence. Car battery keeps draining: evidence to collectRepeated discharge can be battery condition, charging or an electrical load; test before replacing parts. Tyre-pressure light on: check before resettingA tyre can be unsafe before it looks flat; inspect and set pressures from the handbook before any reset.

What should a UK repair actually cost?

Every cost guide quotes a named UK source with the date we read it, never an average we invented. A car MOT in Great Britain cannot cost more than £54.85. A diagnostic sits around £52–£65. A catalytic converter is usually £200–£900 fitted. Only a written estimate for your vehicle is a price.

Car diagnostic test cost: compare the scopeUK booking marketplaces currently publish diagnostic averages of about £52–£65. DPF cleaning cost: what a quote should proveAsk for soot, ash and pressure evidence and the fault that prevented regeneration before authorising work. Clutch replacement cost: compare complete quotesThe RAC, citing FixMyCar in July 2026, puts a typical UK clutch replacement around £670. Brake pads and discs cost: compare axle quotesFixMyCar’s current marketplace averages: pads and discs £266; all-round front and rear pads and discs £555. Cambelt and water-pump cost: define the jobUse the exact engine and maintenance schedule, then compare kit, pump, coolant and warranty scope. Wet-belt replacement cost: check the full scopeThe exact engine, approved oil, debris inspection and oil-system checks determine whether quotes are comparable. Alternator replacement cost: prove the charging faultBattery, belt, cable and control faults can imitate alternator failure, so compare diagnosis as well as parts. Car battery replacement cost: compare like for likeFixMyCar’s current marketplace average for a fitted car-battery replacement is £217. Timing-chain replacement cost: confirm the evidenceNoise or a correlation code alone may not prove chain wear; ask what tests and complete-kit scope support the quote. Catalytic-converter replacement cost: diagnose firstFixMyCar currently says a catalytic-converter replacement usually costs £200–£900 fitted. Wheel-bearing replacement cost: identify the cornerTyre noise can imitate bearing noise; ask how the affected wheel and bearing or hub assembly were confirmed. Head-gasket repair cost: confirm before strip-downAsk for converging test evidence and a clear process for authorising machining or additional engine damage.

When does a car problem stop being a repair and become a safety decision?

Some faults stop being a repair decision and become a safety decision. A flashing engine management light, a pedal that sinks, overheating, exhaust fumes in the cabin or anything hanging under the car all mean stop rather than drive to a garage. These guides say which symptoms cross that line and what to do at the roadside.

When a repair or vehicle problem escalatesFind the next reviewed route by situation: evidence, complaints, ADR, court, recovery or deciding not to repair. Appeal an MOT test result in Great Britain (DVSA)This guide covers the DVSA appeal route for vehicles tested in Great Britain (England, Scotland and Wales): discuss the result with the centre first and send form VT17 within the published deadline, which is 14 working days for a fail. Vehicles tested in Northern Ireland use the separate DVA route on nidirect, where a post-departure appeal must be made within 14 days. How to check a repair garage before you book: Great Britain and Northern IrelandCheck the repair business and the person who will do specialist work, then get the scope and price in writing. For MOT testing, use the DVSA active-station list only in England, Scotland or Wales. In Northern Ireland the DVA, not repair garages, operates the test-centre network; use nidirect for testing and check any repairer separately. A live directory entry or badge is evidence within that scheme’s stated scope, not a guarantee that a diagnosis or quote is right. Complaining about an MOT test station: what DVSA will and will not doDVSA regulates MOT testing standards but does not represent you in a money dispute. In England, Scotland and Wales, suspected lawbreaking or fraud by an MOT tester has a separate route that can be used anonymously. Ordinary disciplinary casework is not promised to the reporter; feedback can be requested only about a criminal prosecution, after the investigation, proceedings and any verdict appeal have ended. How to complain to a garage in writingThe same fault is back and the garage wants more money. Before you argue at the counter, put the complaint in writing: what went wrong, what you want done, and by when. That letter is the record every later step is built on. Diagnostic fees and what they actually coverTreat a fault code as a starting point rather than proof that a named part failed. Before handing over the keys, agree the diagnostic scope, price basis, time limit and written record. A diagnostic charge does not by itself guarantee that the garage will identify or fix the cause. Driving with a dangerous defect: what the law says‘Dangerous’ is an official MOT defect category, and GOV.UK says a vehicle with a dangerous problem has to be repaired before you can drive it. Separately, the law requires the vehicle to be safe at all times, whether or not it has a current MOT certificate. Electric and hybrid high-voltage work: who should be doing itA high-voltage system can be fatal to touch, can hold a dangerous voltage after the vehicle is switched off, and can catch fire long after a knock. Check the named person’s evidence for the exact job rather than relying on a badge alone. A burning smell, hissing, smoke or vapour means stop in a place of relative safety if possible and call 999; do not make an unsafe exit into traffic, and use the matching Great Britain or Northern Ireland road branch below. Estimates, quotes and extra work: authorising a garage repairThe garage has just named a figure that feels too high, and you are still at the counter. Before you hand over the keys, ask whether that figure can move, what it includes, and get the same number in a text or email. This page does not publish a going rate for that bill. Independent inspection reports when you and the garage disagreeAn independent inspection gives you evidence about what is wrong and whether the work was done properly. It does not settle the argument by itself, and nobody can promise that the cost will be repaid to you. If your insurer writes the car off: total loss categories and what followsA write-off is your insurer deciding to pay you the vehicle's value instead of repairing it. The category it is given decides whether the vehicle can ever go back on the road, and the decision follows the vehicle for the rest of its life. If you disagree, your argument is with the insurer, not the garage. Keeping records and evidence after a repair goes wrongA repair dispute is easier for a garage, an ombudsman or a court to check when dated documents are organised into a timeline that another person can follow and, where necessary, question. Start the file when the symptom first appears rather than waiting until you decide to complain, because details become harder to recall with time. Taking a garage to court for money in England and WalesA money claim is the last step, not the first. Put the complaint in writing, give the garage a real chance to put it right, and try mediation or an ombudsman before you pay a court fee. If you do claim, GOV.UK runs the official online route; the fee depends on how much you are claiming, and winning a judgment is a separate thing from actually being paid. MOT retests in Great Britain and the official UK safety-recall checkFor vehicles tested in Great Britain (England, Scotland and Wales), where the vehicle is repaired, when it returns and which items failed decide whether the DVSA MOT route is a free partial retest, a chargeable partial retest or a new full test. Northern Ireland uses separate DVA deadlines: apply for a retest within 21 days of the original test and complete it within 60 days. The official safety-recall lookup is a separate shared UK service. Alternative dispute resolution after a garage complaint failsThe garage has said no, or said nothing. Before you fill in an ombudsman form, check that the garage is actually in that scheme. Most motor schemes only hear complaints about their own members. Get a final response, then read that scheme's current rules. Paying a garage by card: section 75 and chargebackYou paid the garage by card and the repair is wrong. The card company may be a second door, not a replacement for the garage. Credit card and debit card are different routes. Keep the invoice and the written complaint before you phone the card provider. The car cannot be driven: recovery, agreeing the destination and getting homeThis guide separates the official Great Britain and Northern Ireland roadside branches from the later recovery arrangements. Once everyone is out of danger, confirm and agree the destination in writing before loading, within your cover, any police or road-authority arrangement, and the options that are safe and feasible. Replacement parts: what a garage can fit and what you can ask forYou can ask which category of part is going in, ask for it on the paperwork, and ask the garage to keep what comes off. Where a garage supplies the part as well as the labour, the job may be a mixed contract, with goods rules covering the part and service rules covering the work. What a non-original part does to a manufacturer or extended warranty is a question for the warranty terms and the warranty provider, in writing, before the work happens. Scrapping a vehicle at an authorised treatment facilityCheck the ATF on the official register for the nation the vehicle is in, give it the log book but keep the yellow motor-trade section, and notify DVLA. You get a certificate of destruction only if the ATF completely scraps an eligible vehicle. If it repairs and resells the vehicle, no certificate is issued: use the transfer route and keep DVLA's confirmation instead. Keep that confirmation, and the certificate where one is due, as evidence that your responsibility has ended; collection alone is not enough. Selling or part-exchanging a car with a known faultYou know the car has a fault and someone wants to buy it. Put that fault in the advert and on a signed receipt as evidence, not as a magic legal shield. Great Britain and Northern Ireland have separate rules against supplying an unroadworthy vehicle. Do not let an unsafe car be driven away. Taking a garage to court in Scotland: Simple ProcedureScotland does not have a small claims court in the English sense. If a garage owes you money and talking to them has failed, the route is a Simple Procedure claim in the sheriff court, made through the Scottish Courts and Tribunals Service Civil Online portal. It is designed to be quick, cheap and informal, you do not need a solicitor, and the court expects you to have tried to settle first. Everything on this page is Scottish: the names, the forms, the money limit, the rules on expenses and the time limits are all different from England and Wales. Taking a garage to the small claims court in Northern IrelandNorthern Ireland has its own small claims process, run by the County Court through the Northern Ireland Courts and Tribunals Service. You apply online through the Department of Justice or on paper, you pay a fee based on how much you are claiming, and the court decides who is liable rather than paying you itself. Try to settle with the garage in writing first, and get free consumer advice from Consumerline before you spend a court fee. The car is off the road: SORN, vehicle tax and what you must do while it sits thereA car that is stuck waiting for a repair is still a registered vehicle, and doing nothing is the one option that costs money. GOV.UK gives you two lawful states: taxed and insured, or declared off the road with a SORN and kept off public roads. A SORN stops the tax and refunds the full months left, but it also means the vehicle cannot legally stand on the road outside your house. Vehicle testing (MOT) in Northern Ireland: how it differs from Great BritainNorthern Ireland does not use the Great Britain (England, Scotland and Wales) MOT system. Tests are booked with the Driver and Vehicle Agency and carried out at its own test centres, the retest deadlines are counted differently, and disagreeing with a result goes to the DVA rather than to DVSA. Warranties, extended warranty products and goodwill after a repairThe garage says it is out of warranty, or offers a goodwill gesture. Before you accept that as the last word, work out which door you are knocking on: a free guarantee, a warranty you paid for, your statutory repair rights, or a request for goodwill. Those four are not interchangeable. When a garage will not release your car until the bill is paidThe job is done and they will not give you the keys until you pay a bill you dispute. Treat getting the car back and arguing about the money as two separate problems. This page does not decide whether that garage may keep that car. Get advice on your own facts early. When the repair costs more than the car is worthThis guide compares four broad routes; it does not exhaust every contract, insurance or finance option. Choose one comparison horizon that fits your circumstances and use it consistently. Twelve months is an optional worksheet period, not a valuation formula. This page will not value your car or tell you to replace it. Your rights after a car repair goes wrongThe repair did not fix it and you want to know what you can actually ask for. Start with the garage, in writing. What you ask for depends on what went wrong — bad work, a broken promise, a late job, or a disputed bill — and repeat performance is not the first step in every case.

What do you need to know about the MOT, fault codes and basic maintenance?

The MOT tells you what a tester saw on one day, and a fault code tells you which monitor failed. Neither proves a part has broken, and neither is a clean bill of health. These guides cover what the certificate does and does not prove, how retests and fees work, and how to check a garage before you book.

2009 Renault OBD2 Scanner Powers Up but Won't Communicate: Checks to MakeCheck the VIN-specific fuse, socket grounds, connector terminals and Renault protocol before replacing parts. Lifetime scanner updates: are they worth the premium at £200–£400?Compare UK hardware prices, renewal costs, coverage limits and ownership horizons before paying extra for lifetime software updates. Choosing an OBD-II reader: limits before featuresA reader can preserve fault evidence; it cannot prove which part has failed. Car battery health check: safe observations firstStarting symptoms and voltage are clues; a capacity and charging test is needed before replacing parts. MOT advisories explained: what the result does and does not proveAn advisory records an issue seen at the test; it is not a promise that the item will remain safe. Great Britain MOT maximum fee and partial-retest rulesIn England, Scotland and Wales, the maximum car-test fee is £54.85; the Great Britain partial-retest rules determine whether a retest is free or discounted. Pre-MOT checklist: observation-only checksCheck visible items without dismantling, lifting the car or masking warning lamps.

What do these guides say a UK job costs?

These are the published figures the cost guides are built on, with the source each one came from. They are planning ranges for the UK as a whole, not a quote for your vehicle, and each guide records the date the figure was read. A written estimate for your car is the only number that binds anyone.

JobPublished UK figureSourceGuide
Car MOT testMaximum £54.85 in Great BritainDVSA statutory maximum feeMOT cost
DiagnosticAbout £52–£65UK marketplace averagesDiagnostic test cost
Catalytic converter replacementUsually £200–£900 fitted; £509.20 averageFixMyCarCatalytic converter cost

Where do the figures in these guides come from?

Two kinds of source, and each guide says which it used. Statistics are computed from DVSA open data published under the Open Government Licence. Prices are quoted from a named UK commercial source with the date we read it. Nothing on this site publishes a figure that cannot be traced back to one of them.

General guidance, not professional advice.