What to Check When Buying a Used Car: The Full Guide
Most of a used-car check is available to anyone — it takes attention, daylight and about ninety minutes. Below is a 15-minute quick list and the full 145-point protocol we use ourselves: for every section, what to look at with your own eyes, plus honest notes on where equipment is unavoidable.
The 15-minute quick check: top 10
- VIN in the documents = VIN on the body and the plate (any mismatch — walk away)
- Panel gaps and paint tone in daylight — unevenness betrays body repair
- Glass markings on every window: the year should match; one “fresh” window deserves a question
- Tyre DOT codes (week/year of manufacture) and even tread wear
- Pedal, steering wheel and driver-seat wear — does it match the claimed mileage?
- Oil filler cap: light “mayonnaise” emulsion is a head-gasket warning sign
- Cold start: smoke colour, knocks or whistles in the first seconds
- All the electrics in a row: windows, climate, multimedia, cameras, parking sensors
- Test drive: pulling to one side, vibration at 80–120 km/h, how the gearbox shifts
- IPO inspection history (the odometer is recorded at every test) and service records
Handy to take with you in print: Download the printable checklist
How to check up a car before purchase: step by step
The same order works for a do-it-yourself check and for a professional check-up of a car before buying — only the equipment changes.
- Documents before you drive out. Ask for photos of the DUA and the last IPO certificate: match the VIN, year, owners and the mileage recorded at each inspection. A mismatch is a reason not to go.
- Body in daylight. Panel gaps, paint shade, glass markings, tyre DOT codes. This is where the paint gauge earns its keep: a colour-matched respray is invisible to the eye.
- Interior and electrics. Wear on the wheel, pedals and seat against the mileage; every button in turn; mats and the spare-wheel well for signs of water.
- Cold start and under the bonnet. Smoke colour, unusual noises, emulsion under the oil cap, a suspiciously freshly washed engine bay.
- A 20–30 minute test drive. Motorway and town: pulling to one side, vibration at 80–120 km/h, gearbox under load, braking with hands off the wheel.
- Decision and negotiation. What you found is a list of arguments: price the repairs and negotiate from that figure, not from the asking price.
The full protocol: 145 points in 11 sections
Open a section — inside is the full point list plus tips on checking each area yourself.
1. DOCUMENTS (7)
Match the VIN everywhere it appears: documents (DUA), body, plate. Ask for the IPO history — in Portugal the odometer is recorded at every inspection, the best free mileage-fraud detector.
- VIN matches: docs, body, plate
- Registration (DUA) — original
- IPO book — dates, validity
- Service book — records, dealer stamps
- Number of owners
- Both key sets present
- Theft, lien, restriction check
2. BODY — PAINT GAUGE (17)
The one section eyes cannot cover: factory paint is 80–160 µm, a respray is usually 160+. A colour-matched respray is invisible even to a trained eye without a gauge.
- Roof
- Hood
- Front left fender
- Front right fender
- Front left door
- Front right door
- Rear left door
- Rear right door
- Rear left fender
- Rear right fender
- Trunk/tailgate
- Front bumper
- Rear bumper
- Left sill
- Right sill
- A/B/C pillars left
- A/B/C pillars right
In a professional report this section is a table of readings for every panel — see the sample below.
3. BODY — VISUAL (15)
Sight along the body against the light: orange peel, dust in the lacquer, runs. Open doors and bonnet — tool marks on bolts and hinges, sealant that isn't factory-shaped.
- Panel gaps — uniformity
- Repaint signs — orange peel, runs, dust
- Color mismatch between panels
- Weld seams — factory or repair
- Sealant in trunk/hood — factory
- Door/hood hinges — removal signs
- Fender bolts — unscrewing signs
- Glass markings — same date/maker
- Windshield — chips, cracks, replaced
- Rear glass — defroster, integrity
- Door seals — paint traces
- Corrosion — sills, arches, underside
- Corrosion — door cavities, trunk lid
- Underside — protection, impacts, rust
- Wheel arch liners — presence, mounts
4. LIGHTS & GLASS (8)
Headlights should carry the same markings and age evenly. Mismatched lights mean a replacement — ask why (accident?).
- Headlights — markings, date matching
- Headlights — clouding, moisture
- Tail lights — cracks, moisture, replaced
- Fog lights — working
- Turn signals — all working
- Brake lights — all working
- Reverse light
- License plate light
5. TIRES & WHEELS (9)
Four matching tyres are the sign of a cared-for car. Mixed brands and years mean savings were made. The DOT code reads right off the sidewall.
- Tire brand — all 4 matching
- Tire manufacture date (DOT)
- Tread depth — uniformity
- Uneven wear (inner/outer)
- Cracks, bulges, sidewall cuts
- Size matches factory spec
- Wheels — cracks, deformation, repair
- Spare tire — present, pressure
- Jack and wrench
6. INTERIOR (24)
Your nose finds damp and mould faster than your eyes. Lift the mats, check the spare-wheel well — flood damage shows there first.
- Smell — damp, mold, oil, smoke
- Moisture — under mats, in trunk
- Steering wheel — material wear
- Pedals — wear matches mileage?
- Driver seat — bolster wear
- Seatbelts — condition, date tag
- Airbags — indicator, covers intact
- Headliner — sagging, stains
- Climate control — all modes
- A/C — cooling, smell
- Heater — all fan speeds
- Power windows — all 4
- Mirrors — adjust, heat, fold
- Heated seats (if equipped)
- Power seat adjust (if equipped)
- Sunroof — open, close, seal
- Multimedia — screen, sound, inputs
- Bluetooth — pairing, hands-free
- Navigation — working
- Rearview camera / parking sensors
- USB/AUX ports
- 12V socket
- Central locking — all doors
- Wipers and washer — all modes
7. UNDER THE HOOD (13)
Check with the engine cold: oil level and colour, emulsion under the cap, coolant level, signs of a freshly washed bay (a common way to hide leaks).
- Burnt oil/coolant smell
- Leaks — oil, coolant, PS, brake
- Engine oil — level, color, emulsion on cap
- Coolant — level, color, purity
- Brake fluid — level, color
- PS fluid — level
- Battery — age, terminals, corrosion
- Timing belt/chain — when replaced
- Drive belts — cracks, tension
- Hoses — cracks, clamps, leaks
- Non-standard repair signs
- Non-original parts visible
- VIN on body — legibility, tampering
8. ENGINE START (10)
Start it yourself, from cold. Blue smoke — oil; thick white — coolant; black — fuelling. A knock or whistle in the first seconds calls for deeper diagnostics.
- Cold start — first try?
- Blue smoke (oil)
- White smoke (coolant)
- Black smoke (fuel)
- Unusual noises at start (knock, whistle)
- Knock persists after warm-up?
- Idle stability
- Engine vibration at idle
- All indicators off after start?
- Check Engine light — off?
9. OBD DIAGNOSTICS (7)
Even a cheap OBD dongle shows current faults. Stored faults, module mileages and live data need a proper scanner.
- Engine errors — current
- Engine errors — stored (history)
- Transmission errors
- ABS / ESP errors
- Airbag errors
- Mileage across ECUs — matches?
- Live Data — sensors normal
We read the modules with a Launch scanner and hand the client the full log — the sample report shows what that looks like.
10. TEST DRIVE (18)
At least 20–30 minutes including highway: acceleration, braking with hands off the wheel, pulling, vibration at speed, gearbox behaviour under load.
- Auto trans — no delay engaging
- Auto trans — smooth shifts
- Auto trans — no jerks or slipping
- Manual — easy shifting
- Manual — clutch: travel, bite point
- Manual — clutch pedal no pulsation
- Acceleration — no hesitation
- Steering — play
- Pulls to one side straight
- Wanders left-right
- Vibration at 80-120 km/h
- Humming at speed (bearings)
- Brakes — effectiveness
- Brakes — pedal pulsation
- Brakes — pulling to side
- Steering shake when braking
- Suspension knocks/squeaks on bumps
- Shock absorbers — body bouncing
11. LIFT INSPECTION (17)
Underbody, brakes from the inside, drivetrain leaks, suspension from below — physically impossible without a pit or a lift.
- Underside — corrosion, impacts, protection
- Exhaust system — integrity, mounts
- Front brake pads — remaining
- Rear brake pads — remaining
- Brake discs — wear, grooves, cracks
- Brake hoses
- CV joint boots — integrity
- Tie rod ends — play
- Tie rods — condition
- Ball joints — play
- Bushings — cracks, wear
- Shock absorbers — leaks
- Springs — sagging, cracks
- Stabilizer — links, bushings
- Subframe — mounts, corrosion
- Gearbox — oil leaks
- Differential / driveshaft (AWD)
This is a separate 17-point block: with us it is +€100 on top of the inspection, arranged in advance.
📄 What this looks like in a professional report
So you have something to compare against: download an anonymised sample of a real report — paint readings per panel, findings, verdict and photos. Free, and useful even for a fully DIY check.
Download the sample report (PDF)When to call a professional
The honest criterion is not “always” — it is these situations:
- The car is in another city — the trip and a day off cost more than the check
- No paint gauge and no scanner — the two key sections stay blind
- An expensive car: the cost of a mistake is many times the cost of a check
- The seller is rushing you (“three more people are coming”) — classic pressure
- You don't speak Portuguese and the seller speaks nothing else
Frequently asked questions
Can you properly check a car without any tools?
About seventy percent of it, yes: documents, gaps, glass, tyres, interior, start-up, test drive. Two zones stay blind: paint (a colour-matched respray only shows on a gauge) and electronics (stored faults and module mileages need a scanner).
How long does a DIY check take?
The full protocol takes 1.5–2 hours. Short on time? Run the top-10 from this guide in 15–20 minutes — it filters the most expensive problems: crash-repaired bodywork and clocked mileage.
What tools should I bring?
A torch, a cloth, gloves and the printed checklist as a minimum. Ideally: a paint-depth gauge (from €30–40) and an OBD dongle (from €20). The famous magnet trick does not work — modern panels are often aluminium or plastic.
What should I check first if I have almost no time?
Five things: VIN match, glass markings, tyre DOT codes, emulsion under the oil cap and how the car behaves on a test drive. Those five minutes filter out most of the dangerous cars.
Isn't a valid IPO (Portuguese MOT) proof of condition?
No. The IPO checks minimum safety requirements — brakes, lights, emissions. Paint, crash repairs, engine and gearbox condition are not part of it: a car with a fresh IPO can still be a rebuilt wreck.
Checked it yourself and still in doubt?
Send the listing link on WhatsApp — we'll tell you honestly whether the car deserves attention, and come out with the gauge and scanner if needed.
