Reading MOT advisories on a used car before you buy

Every used car advert says "long MOT". That tells you when the next test is due. It tells you nothing about what the tester actually wrote down last time, and that's where the useful stuff lives.

The good news is it's free to look. Put the reg into the GOV.UK "Check MOT history" service and you'll get every test since the car's first one, usually at three years old in Great Britain. Each line shows the date, the mileage, the result and any notes. Ten minutes on that page before a viewing can save you a wasted trip.

The four kinds of note

Since May 2018 the tester sorts problems into four groups.

Dangerous and major defects mean a fail. The car can't pass until they're fixed.

Minor defects are a pass, but they're real faults the tester had to record.

Advisories are a pass too. They're the "keep an eye on this" notes: things that aren't bad enough to fail today but could be by next year.

People tend to skim past advisories because the result says PASS in green. That's a mistake. Advisories are the closest thing you'll get to a mechanic's honest opinion of the car, written by someone who had it up on a ramp and had no reason to flatter it.

What to look for

The same advisory, year after year. "Front brake disc worn, pitted or scored" once is normal wear. The same line three years running means nobody bothered, and you're the one who'll be paying for discs and pads before long.

Corrosion notes. "Underside corroded but not seriously weakened" is common on older cars and often fine. Watch for it moving to brake pipes, sills or suspension mounts, or for wording that gets worse over time. Rust doesn't go backwards.

Tyres near the limit. The legal minimum is 1.6mm across the central three quarters of the tread. An advisory saying a tyre is close to that means budgeting for new tyres soon, ideally before winter.

Oil leaks. "Oil leak, but not excessive" can be a cheap gasket or a sign of something bigger. It's worth asking whether it's been looked at since.

Advisories that vanish. If something was flagged last year and isn't there now, that's usually good news, because it was probably fixed. Ask for the invoice. A seller who did the work will normally have it.

Don't forget the mileage column

While you're there, read down the mileage figures. They should go up steadily. A reading that's lower than the one before, or a sudden jump after years of low use, isn't proof of anything on its own (typos and replaced clusters happen) but it's a question the seller should be able to answer.

Turning notes into questions

Here's how I'd use it. Before the viewing, write down every advisory from the last two tests. At the car, ask about each one directly. "Last year's MOT flagged the rear brake pipes. Have they been done?" is a far better question than "any problems with it?", and the answer tells you a lot about how the car's been looked after.

If the wording confuses you, the free MOT advisory decoder from CarCheckHQ lets you paste a line in and see which part it covers and what would turn it into a fail. And if you want a ready list of questions to take along, their ask-the-seller checklist builds one for you.

What MOT history won't tell you

An MOT only checks roadworthiness on the day. It won't show outstanding finance, whether the car has been written off, or whether it's been reported stolen. That's what a full history check is for, and it's worth doing once you're serious about a particular car.

The takeaway

A green PASS is the start of the story, not the end. Read the advisories, check that the mileage climbs, turn every note into a question, and walk away from any seller who gets cagey about simple answers. It's ten minutes of reading for a car you might keep for years.