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Welcome to the latest in a series of posts we’re putting together on what MOT data can tell us about which cars you should be looking at when buying used. We’ve carried out an analysis of the MOT history data published by the government and have discovered some interesting things about the condition of the cars that are on Britain’s roads today.

This time we’re looking at large family cars like the BMW 3 Series, Audi A4, and Mercedes C Class. So, if you’re wondering what’s the most reliable family car you’ve come to the right place to get your question answered.

Here at CarXpert we’ve created a unique way of rating cars based on their MOT history. We give cars a rating of between one and five stars based on their MOT failures, MOT advisories, and overall MOT history.

A car’s MOT history can give you a good idea of both its condition and how well it’s been looked after. If you have a used car that you’re considering, enter the registration number here and CarXpert will give you its ratings. And it’s free!

How We’ve Calculated Our Rankings

We’ve analysed MOT results for cars that are between 6 and 12 years old using our CarXpert algorithms. We used this age range because we’re assuming that people tend to keep their cars for a few years so would like to know which are the best cars over a period of time.

We’ve looked at items that have caused cars to fail their MOTs and also advisory items that owners have been made aware of by MOT testers. CarXpert’s algorithms gives each car a star rating for Failures and Advisories, and then we’ve looked at the average ratings for both for each make and model.

How CarXpert’s Star Ratings Work

CarXpert has analysed huge amounts of data about MOT results and can rate cars on a 1 to 5 star scale in terms of how good their MOT results are compared to cars of the same age:

• For a car to get five stars it must have had zero failure or advisories – nothing has ever been reported by an MOT tester
• A four star car is one with better than average MOT results – some issues have been found during MOTs, but fewer than the typical number
• A three star car is around the average for MOT results – this car has had about the number of issues found that would be expected
• A two star car is worse than average for MOT results – more issues have been found during MOTs than would be expected
• A car that only gets one star has much worse than average MOT results – a lot more issues have been found at MOTs than would be expected

How We’ve Identified Issues To Look Out For

As well as ranking each make and model, we’ve also used CarXpert’s technology to analyse what items typically cause each type of car to fail MOTs, and therefore what you should be looking out for if you’re thinking of buying one. The most common reasons that all types of cars fail MOTs on are normal wear and tear items like tyres, wiper blades or bulbs, but there are usually issues that occur more frequently on particular types of car, and it’s those that we’ve highlighted for each car in our list.

So, without further ado, here’s our ranking of the five best large family cars.

1. Audi A4/A5

In first place we have Audi’s A4 and A5 models with an average CarXpert rating of 3.44

We’ve put the A4 and A5 together because they are essentially different versions of the same model of car, the A5 being the coupe version. Here’s a breakdown of what percentage of Audi’s are in each of our 1 to 5 star categories –

Outside of the usual reasons cars trip up on an MOT test like tyres and lights, there are a few things that you need to watch out for on these Audis.

Rear Shock absorbers can cause MOT failures more than is typical, so check the MOT history of any car that you’re considering for an advisories that mention leaks from shock absorbers or reduced efficiency. You can look at the MOT history of any car that you rate with CarXpert here.

The engine management light can stay on, indicating a problem – and that’s an MOT fail. If you’re looking at a used Audi make sure the engine management light comes on with the ignition and goes out once the car has started.

These Audis seem prone to wheel fractures, often by the valve, so have a good look at the condition of the wheels when you’re looking at one.

Number plates not conforming to the regulations will cause a car to fail its MOT, and this seems to be unusually common with these cars. If you’re looking at buying a used Audi with a personalised plate, make sure that the letter spacing isn’t odd, or that coloured screw covers haven’t been used to try and give the impression that a number is a letter.

Headlamp levelling devices have been known to fail, so turn on the headlamps and change the switch position; it should move the headlamp beam up and down.

If you’ve like more information about the different versions of A4 and A5, engine choices and specifications, here’s a link to a buyer’s guide.

2. Mercedes C Class

In second place is the Mercedes C Class – which also got an average CarXpert rating of 3.44, and it’s only behind the Audi if you look at the rating to 3 decimal places, so there’s very little in it.

The chart below shows you how the C class did in terms of the proportion of cars in each of our categories –

Apart from the usual MOT items, we saw a few things come up about the C Class when we analysed the data.

Brake pipes can show damage or signs of corrosion. Something to look out for in the MOT history as it’s not easy to check when looking at a car you’re considering.

While lights not working are a common cause of MOT failures, faulty direction indicators are reported much more frequently on C Classes than other cars, so make sure these are working properly.

Check the wheels for any cracks or fractures, and while you’re looking at the wheels make sure that all the wheel bolts are present and correct as these seem to go missing more than is typical.

As with the Audis, number plates can cause MOT failures on these Mercedes if they’re not laid out in the way that the regulations specify.

Check that the ESC (Electronic Stability Control) light comes on with the ignition and goes off once the engine is running as that would be an MOT failure because it suggests there’s a problem with the stability control.

Here’s a link to a buying guide to the C Class that will give you additional information about this Mercedes

3. BMW 3 Series

In third place we have BMW’s 3 series with an average CarXpert rating of 3.41. While the BMW 4 Series is the coupe and convertible relative of the 3 Series, we didn’t include them in the rating because they haven’t been on sale long enough to provide enough representative data for older cars.

So, what to look out for if you’re considering a 3 Series?

Shock absorbers, both front and rear, can fail more than average, so have a look at the MOT History and see if there’s any mention of problems with the shock absorbers.

As with the Mercedes, check the wheels for loose or missing wheel bolts and for wheel fractures.

Once again, modified number plates crop up more than average as an MOT failure, so check the number plate hasn’t had the spacing of the letters changed or otherwise doesn’t look like a normal plate.

Check that the ABS warning light comes on with the ignition and goes out when the engine has been started. If it doesn’t then it indicates a fault. The same checks apply to the ESC (Electronic Stability Control) light for the same reason.

Petrol engine “Lambda coefficient outside the default limits or the range specified by the manufacturer” and “Emissions levels exceed default limits”

Make sure the headlamp washers are working as these became an MOT test item in 2018, and the 3 Series appears to have faulty headlamp washers more frequently than other cars.

If you want information about versions, equipment or running costs, here’s a link to a 3 Series buying guide.

4. TOYOTA AVENSIS

Coming in at fourth place is the Toyota Avensis, with an average CarXpert rating of 3.37

If you’re considering an Avensis for your next car, here’s a few suggestions of what to look out for based on our analysis of MOT histories.

Brakes seem to be a weak area for the Avensis with a variety of problems being mentioned. Among the more serious, brake pipes have a tendency to corrode, and leaks can occur in the braking system – both particularly at the rear. Check the MOT history for any mentions of the braking system, check the brake fluid level is ok, and give the brakes a good workout during a test drive for any Avensis you’re considering.

Avensis’s can suffer from problems with the Electronic Stability Control, so check that the ESC light comes on with the ignition and goes off once the engine is running.

Something that you need to look at the MOT history for is any mention of front suspension component corrosion as this crops up on Avensis’s more than is usual. If severe enough this can lead to an MOT failure.

Here’s a link to a buyer’s guide for the Avensis if you’d like more information about equipment, versions and engine choices.

5. Skoda Superb

In fifth place we have the Skoda Superb with an average CarXpert rating of 3.35.

Here’s how the CarXpert star ratings are distributed for the Superb –

Like the other cars in this list, Superbs do better than other large family cars, but there are some things to be aware of if you’re looking at a used Superb.

Front suspension joints can wear, so check the MOT history for any mentions in that area, and listen for any clonking or knocking noises from the front of the car on the test drive.

As with the Mercedes, an unusually high proportion of Superbs fail MOTs due to problems with the direction indicators, so make sure they are working properly.

Check that the SRS (Supplementary Restraint System / airbag) light comes on with the ignition and goes out when the car starts. If that’s not the case, it’s an MOT fail and indicates a problem with the airbag system.

Headlamp levelling can play up, so make sure that the headlamp levelling switch has an effect on the headlamp beam.

Diesel Superbs can fail their MOTs because of excessive smoke from the exhaust, so try revving the engine at a standstill and keep an eye on the rear-view mirror during the test drive to make sure that there isn’t a lot of black smoke appearing.

More information on the Superb can be found in this buyer’s guide.

We hope you found this post helpful, and if you have any feedback it would be great to hear about it in the comments.