Pre-Purchase Inspection Checklist: Avoid Fraud & Hidden Damage (2026 Guide)

The first car I ever inspected for someone else was a 2014 Golf TDI listed at 78,000 km for €11,500. Looked great in the photos. Looked great in person. I plugged in the scanner, pulled zero codes, and almost said it was clean. Then I checked the readiness monitors: all eight showing "not ready." Someone had cleared the codes less than a day before. I told the buyer to walk away. He didn't listen, bought it anyway, and had a €1,800 DPF replacement within six weeks.

That's the kind of story this guide exists to prevent. A pre-purchase inspection isn't paranoia. It's the difference between buying a car and buying someone else's problem. And you don't need to be a mechanic to do a thorough one. You need your eyes, your nose, a few cheap tools, and some knowledge about what the car's own computer is trying to tell you.

What to Bring

You don't need a rolling tool chest. Here's what actually matters: your phone (for photos and notes), an OBD2 Bluetooth adapter, a small flashlight, and a tyre pressure gauge. That's it. If you've got a diagnostic app like Skanyx loaded on your phone, you're already ahead of most buyers.

One thing people get wrong: don't plug in the OBD2 adapter with the engine running. Connect it with the ignition off, then turn the key to the ON position (or press the start button without your foot on the brake, for push-button cars). This lets you pull stored data cleanly before the engine muddies things up with a fresh startup cycle.

Also bring a friend if you can. Not for moral support. For a second pair of eyes. It's remarkably easy to miss a paint mismatch or a weird smell when you're excited about a car.

Start With Your Eyes, Ears, and Nose

Here's something that surprises people: an OBD2 scan can't tell you about most of the things that make a used car a nightmare. It can't see rust. It can't feel worn brake pads. It can't smell the mould growing under the carpet from a flood two years ago. The diagnostic scan is powerful, but it's one layer of the inspection, not a replacement for a physical walkaround.

The Exterior

Walk around the car slowly, ideally in daylight. You're looking for panel gaps that don't match side to side: a door that sits slightly higher than its neighbour, a fender that sticks out a few millimetres more than the one opposite. These are signs the car has been in a collision and had body panels replaced or pulled back into shape.

Look at the paint from a shallow angle. Does one panel have a slightly different shade than the one next to it? Fresh paint on a single panel almost always means accident repair. Run your hand along the edges of the hood, boot, and doors. Factory paint is smooth and uniform. Repainted panels often feel slightly different in texture, especially around edges and underneath.

If you're buying cars regularly or looking at anything over €15,000, a paint thickness gauge (€30-€80) is worth having. It measures paint depth in microns: factory paint is typically 100-140 microns. Repainted panels read 200+ microns. It turns "I think this panel looks different" into "this panel has been repainted, here's the data."

Check the tyres. Uneven wear across a single tyre suggests alignment problems, which in turn can mean bent suspension components from an impact. If all four tyres are brand new on a car that supposedly hasn't been in an accident, ask yourself why. Check the DOT code on the tyre sidewall (4-digit number, e.g., 2419 = week 24 of 2019). Brand-new tyres on a "low-mileage" car? Ask why the originals needed replacing.

Look at every piece of glass. Factory glass has a logo with the car manufacturer's name. If one window has a different brand, it's been replaced. That's not always sinister (rocks happen) but it's worth noting, especially if the seller claims the car has never been damaged.

Under the Hood

Pop the hood and look before you touch anything. Are the fluids at the right levels? Oil should be between the marks on the dipstick. Coolant should be at the full line when cold. Transmission fluid (on cars that have a dipstick for it) should be pinkish-red, not brown or burnt-smelling.

Look at the belts and hoses. Cracking, fraying, or swelling means they're due for replacement. Not a dealbreaker, but a negotiation point. Check the battery terminals for heavy corrosion. Look at the wiring harnesses: corroded connectors or green-tinged wires in odd places can be a sign of water intrusion.

Speaking of water: if you see water stains high up in the engine bay, on the firewall, or around the fuse box, be very cautious. Flood-damaged cars get resold more often than you'd think, and the electrical gremlins they develop can be endless.

The Interior

Sit in the car and just breathe for a moment. I mean that literally. What does it smell like?

I now make a habit of sitting in the car with the windows closed for a full minute before I turn anything on. On a 2016 Audi A3 I was checking, there was a faint sweetness that I couldn't place at first. Not air freshener. Coolant. The heater core was leaking, and the smell was only detectable when the car had been sitting in the sun with the windows up. That's a €600-€900 repair because the entire dashboard has to come out to reach the heater core on most modern cars.

A musty, damp odour suggests water damage or mould. A heavy air freshener can be masking something. Cigarette smoke permeates everything and is nearly impossible to remove completely.

Turn on the air conditioning and put your nose near the vents. Mildew smell from the AC is another flood indicator, or at minimum a sign that the evaporator drain is clogged and has been for a while.

Check that every button, switch, and control actually does what it's supposed to. Power windows, locks, mirrors, seat adjustments, heated seats, sunroof. These are individually cheap problems but they add up fast, and they give you a sense of how well the car has been maintained overall. A car with three broken interior features has probably had maintenance deferred in other areas too.

Look at the pedal pads, the steering wheel, and the driver's seat bolster. These wear at predictable rates. A car claiming 65,000 km shouldn't have a steering wheel that's shiny and worn smooth at the 10 and 2 positions. That's a 190,000 km wheel. Mismatched wear is one of the quieter signs of odometer fraud. For a deeper dive on detecting mileage fraud specifically, including how to read module mismatch data and cross-border laundering patterns, see our odometer fraud detection guide.

The Diagnostic Scan

Now it's time to let the car's computer talk. This is where most people stop at "are there any codes?" and miss the really useful information.

Stored and Active Codes

Active codes (also called current DTCs) mean there's a problem happening right now. Stored codes are problems the car detected previously but that may have resolved or been intermittently present. Both matter. A stored P0420 (catalytic converter efficiency) means that converter is on its way out even if it's not currently tripping the light. Budget €800-€2,200 for that repair.

Transmission codes in the P0700 range are among the most expensive to address. If you see them, get a professional evaluation before proceeding. Multiple misfire codes across different cylinders (P0300 series) suggest systemic engine problems rather than a single failed spark plug.

Pending Codes

This is one most buyers don't know about. Pending codes are problems the car has detected once but hasn't confirmed yet. Think of them as the car whispering about future problems. The engine management system needs to see a fault multiple times before it sets a confirmed code and turns on the check engine light. A pending code means the car noticed something wrong at least once.

If you see pending codes during a pre-purchase inspection, pay attention. They might become full codes in a week. They might not. But they're telling you something the seller probably doesn't know about, and that's valuable information.

Readiness Monitors: The Most Underrated Check

This is the check that separates a cursory scan from a real inspection. Your car's engine management system runs a series of self-tests called readiness monitors. They cover the catalytic converter, oxygen sensors, evaporative emissions system (EVAP), EGR, and several other subsystems. Each monitor runs under specific driving conditions and reports back as either "ready" (test complete, system passed) or "not ready" (test hasn't run yet).

Here's why this matters so much: when someone clears diagnostic codes with a scan tool, it also resets all the readiness monitors to "not ready." The monitors then need various driving cycles (sometimes a week or more of mixed city and highway driving) to complete their tests and flip back to "ready."

So picture this scenario: you scan a car and find zero codes. Great, right? But then you look at the readiness monitors and see that five of them show "not ready." That car had its codes cleared recently, and it hasn't been driven enough for the monitors to complete their checks. The previous codes could have been anything: a failing catalytic converter, an oxygen sensor going bad, a serious emissions problem. You have no way to know, and that's exactly the point. The seller (or the seller's mechanic) didn't want you to know.

Now, one or two incomplete monitors can be perfectly normal. The EVAP monitor is notoriously finicky and often won't complete unless conditions are exactly right: specific temperature range, specific fuel level, specific driving pattern. On some vehicles, the secondary air system monitor takes a long time too. But if you're seeing three, four, five incomplete monitors on a car that's supposedly been driven regularly, someone cleared the codes and hoped you wouldn't look this deep.

There's a recurring thread on motor-talk.de's Gebrauchtwagen (used car) forum where someone posts about a car they inspected that had all readiness monitors reset. Every time, the comments split between "walk away immediately" and "the seller probably didn't know." The experienced members are always in the first camp.

When you see this pattern (no codes but many incomplete monitors) the right move is to either walk away or ask the seller to let you drive the car for a few days so the monitors can complete. If they refuse, you have your answer.

This is one of the first things Skanyx checks during a pre-purchase scan: how many readiness monitors are complete. If you see zero codes but five incomplete monitors, the app flags it immediately and tells you what it likely means. No need to interpret the raw data yourself. skanyx.com/download

Live Data: The Numbers That Tell the Story

Raw code scanning tells you what went wrong. Live data tells you what's happening right now. Here are the parameters worth watching before and during your test drive.

Fuel trims are probably the single most informative live data parameter for a pre-purchase inspection. Short-term fuel trim (STFT) fluctuates constantly as the engine adjusts its fuel mixture in real time. Long-term fuel trim (LTFT) represents the engine's learned correction over time. On a healthy engine, STFT should stay within about plus or minus 5%, and LTFT should be within plus or minus 10%. If you're seeing LTFT at +15% or higher, the engine is consistently running lean, likely from vacuum leaks, a failing mass airflow sensor, or worn fuel injectors. The car might drive fine right now, but that's a problem that's going to get worse. Engine coolant temperature should climb steadily after a cold start and stabilise between 90 and 105°C. If it overshoots and then comes back down, the thermostat might be sticking. If it keeps climbing past 105°C under normal driving, you've got a cooling system issue: could be anything from a failing water pump to a head gasket starting to go. Misfire counts are available on most modern cars through live data. Occasional single-digit misfires can be normal on high-mileage engines, especially at idle. But if you're seeing steady misfires on one or more cylinders, that's a problem regardless of whether a code has set yet. Compare misfire counts across all cylinders: they should be roughly similar. One cylinder misfiring significantly more than the others points to a coil, plug, or injector issue on that specific cylinder.

If running a diagnostic scan while test-driving sounds like a lot to manage, that's exactly what we built the Skanyx PPI for. The app walks you through a guided inspection: initial code scan, 30-second idle test, 2-minute cruise test, acceleration test, and a final code scan. Then the AI analyses everything and generates a report with an overall grade (Pass, Conditional Pass, or Fail), repair cost estimates, and negotiation talking points you can show the seller or your mechanic. €24.99 per inspection, or grab a 3-pack for €59.99 if you're shopping seriously. skanyx.com/download

The Test Drive

Don't just drive around the block. You need at least 20 minutes covering different conditions: stop-and-go, highway speeds, some hills if possible, and a few hard accelerations from a stop. If the seller suggests a specific route, go a different way. They may have chosen a route that avoids the pothole that triggers the suspension clunk or the hill that reveals the transmission's reluctance to downshift.

With your diagnostic app running during the drive, watch the coolant temperature, fuel trims, and RPM. The engine should idle smoothly. The transmission should shift cleanly without hesitation, harshness, or slipping. If you feel the engine briefly rev higher than expected during a shift (like the transmission momentarily lost grip) that's slipping, and transmission work is expensive.

Listen. Turn off the radio. You want to hear the engine, the suspension, the brakes. A rhythmic clicking during turns suggests worn CV joints. A grinding or squealing when braking means the pads or rotors need work. A clunk over bumps points to worn suspension bushings or ball joints. None of these show up on an OBD2 scan, which is exactly why the physical test drive matters alongside the data.

After the drive, do one more scan. Compare the results to your pre-drive scan. Any new codes that appeared during the test drive are significant: the drive stressed the systems enough to reveal problems that sitting in a driveway didn't. Check the readiness monitors again too. If any that were previously "not ready" flipped to "ready," that's actually a good sign: the systems ran their tests and passed.

Reading the Vehicle History Report

Pull a vehicle history report. In Europe, carVertical is the most widely used, with coverage across EU member states. In Belgium, request a Car-Pass (mandatory at sale, €10.40). In the Netherlands, check the NAP register through RDW. In Germany, request TUV/DEKRA inspection records, which log mileage at each HU. In the UK, an HPI Check covers finance, theft, and write-offs. If the car was imported, check the records from the country of origin, not just the current country.

You're looking at a few specific things. First, the mileage history: it should show a steady upward progression at each recorded event. Any drop (say 97,000 km at one service visit and then 72,000 km at the next) is a glaring odometer fraud indicator. For a deeper dive on detecting mileage fraud specifically, including how to read module mismatch data and cross-border laundering patterns, see our odometer fraud detection guide.

Check for title brands. Salvage, rebuilt, flood, and lemon titles all mean the car was deemed a total loss or had serious manufacturer defects at some point. A rebuilt title means someone fixed a totalled car. The repairs might have been excellent or they might have been cosmetic-only: you have no way to know. These titles reduce the car's value by 20-40%, so if the asking price doesn't reflect that, you're overpaying.

Look at ownership history. A car that's had four owners in three years is being passed around for a reason. Long single-owner histories with regular service records are what you want to see.

Cross-Border Purchases: Higher Stakes

If you're buying a car that was imported from another country (common in Lithuania, Poland, Latvia, and across the Baltics, where 50-75% of used cars are imports), the inspection is even more critical. Cars lose documentation during cross-border transfers. Service histories don't always follow the car. And the opportunity to roll back the odometer during transit is well-documented. Treat every import as a car with an unknown history until you can verify it yourself.

What Common PPI Findings Cost to Fix

PPI Options Compared

Red Flags That Mean Walk Away

Some findings aren't negotiation points. They're exit signs.

A seller who refuses to let you inspect the car, or who insists you can't bring your own scanner, is hiding something. Period. There's no innocent explanation for refusing an inspection on a car you're asking thousands of euros for.

On r/UsedCars, the single most upvoted piece of advice in any "should I buy this car" thread is "get a PPI." The second most upvoted is "no, seriously, get a PPI." The people who post regret stories almost always start with "I skipped the inspection because..." followed by an expensive lesson.

Multiple cleared readiness monitors combined with suspiciously zero codes. As we covered above, this almost certainly means the codes were recently cleared.

Any sign of flood damage: musty interior odours, water stains on seats or headliner, corroded wiring connectors, silt or sand in crevices that shouldn't have it, or mildew blowing from the AC vents. Flood cars develop electrical problems for years after the event.

Misaligned body panels, paint colour that doesn't match between adjacent panels, or welding marks on structural components. These indicate collision damage, and structural repairs mean the car's crash protection may be permanently compromised. If you spot signs of major accident repair, check whether the airbags have been replaced: missing airbag badges or mismatched trim around airbag panels suggest the bags deployed and may not have been properly replaced.

"As-Is" Sales and Your Rights

"As-is" deals deserve extra scrutiny. But here's what many buyers don't know: in the EU, if you buy from a dealer (not a private seller), you have a legal guarantee of conformity (EU Directive 2019/771). This means the car must match its description and be free of defects that weren't disclosed at the time of sale. In most EU countries, this guarantee lasts 2 years from purchase. If a defect appears within the first year (6 months in some countries), the seller must prove the defect wasn't present at sale, not the other way around.

Private sales are different. Most EU countries don't require private sellers to offer any guarantee. This is where your PPI matters most, because once the money changes hands in a private sale, your legal options are limited to proving fraud.

When a seller is very insistent that the sale is final the moment you hand over money, consider what they might know that you don't. An as-is private sale isn't automatically a scam, but it should make your inspection even more thorough.

Using Your Findings to Negotiate

Here's where the data pays for itself. If your inspection reveals issues, you now have specific, documented findings to bring to the negotiation table. This isn't about nickelling and diming the seller: it's about pricing the car based on its actual condition rather than its advertised condition.

A stored P0420 code with the catalytic converter efficiency below threshold is worth €800-€2,200 in repair costs. A set of worn brake pads and scored rotors is €250-€500. Tyres with uneven wear that need replacement are €350-€700. These aren't hypothetical: they're real costs you'll incur after purchase.

Best negotiation I've ever seen: a friend ran a full diagnostic scan on a 2017 BMW 320d listed at €16,500. Found a stored P0420, fuel trims at +14% (indicating a developing vacuum leak or MAF issue), and the front brake rotors were scored. She printed the scan results, showed the seller exactly what was there, and offered €13,800. The seller took it. The scan tool cost her €30 and saved her €2,700 on the purchase price alone. She spent about €400 fixing the brakes and is still monitoring the fuel trims.

Present your findings matter-of-factly. "The scan showed a stored catalytic converter code and the fuel trims are running high. I'd like to move forward, but I need the price to reflect the €1,500 or so I'll be putting into repairs." Most sellers will negotiate when faced with specific data rather than vague complaints. And if they won't budge, you have the information you need to decide whether the car is still worth it at the asking price.

In an EU dealer purchase, you can also use your findings to request repairs under the legal guarantee rather than negotiating price. Present the documented issues and ask the dealer to fix them before completion. A dealer who refuses to address documented defects before sale may be creating liability for themselves under EU consumer protection law.

If you want a professional-looking report to bring to the negotiation table, Skanyx's PPI generates a PDF with your findings, AI analysis, cost estimates, and photos. It's harder for a seller to argue with a documented report than with "my friend said the engine sounds weird." skanyx.com/download

Here's an Uncomfortable Truth About Mechanic PPIs

Most independent garages do a visual inspection and a quick code scan. That's it. They don't check readiness monitors. They don't pull pending codes. They don't log live data during a test drive. They look under the car, check the brakes, look at the fluids, and give you a thumbs up or down. For that, you pay €100-€200.

A thorough diagnostic scan that you do yourself with a €30 tool and some knowledge will catch things that most paid PPIs miss. The ideal approach is both: do your own diagnostic scan AND get a mechanic to check the mechanical stuff you can't see (underside, suspension, exhaust).

The "My Mechanic Already Inspected It" Trap

If you're buying from a dealer and they say "our mechanic already inspected it," that inspection was done by someone who works for the seller. Ask for the report. If there isn't one (there usually isn't), that "inspection" was a mechanic glancing at the car on the lot. Always do your own. The seller's mechanic works for the seller, not for you.

Frequently Asked Questions

What's the minimum PPI I should do?

At minimum: a full OBD2 scan for stored, pending, and active codes, plus a check of readiness monitors. Visually inspect the underbody for rust and frame damage, check for fluid leaks, test the brakes and steering, and verify the mileage against a history report. Even a basic inspection like this catches the majority of hidden problems.

Who should pay for the PPI?

The buyer, almost always. It's a small cost (whether you're using your own scan tool or paying a mechanic €100-€250) compared to the €2,000-€7,000 mistakes it can prevent.

Can I skip the PPI on newer or low-mileage cars?

I wouldn't. Flood damage, accidents, and title issues happen to three-year-old cars with 40,000 km just as easily as to ten-year-old cars with 240,000 km. A newer car might even be riskier in some ways, because you're paying more and have more to lose.

What if the seller refuses a PPI?

Walk away. There is no legitimate reason to refuse an inspection. A seller who says "the car's fine, you don't need to check it" is telling you the opposite.

What can OBD2 NOT tell me?

Quite a lot, actually. Brake pad thickness, suspension wear, body rust, tyre condition, interior damage, AC performance, power steering condition, and the visual state of cooling system components are all invisible to the scanner. The OBD2 port connects to the engine and emissions management systems, not to every part of the car. That's why the physical inspection and the scan work together: neither one alone is enough.

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