Reliability Survey: Most and least reliable diesel cars

Diesel cars may have fallen out of favour with the Government and the car buying public in general, but they are still a viable proposition for many drivers.

They can be the best option for high-mileage motorway motorists because they’re usually more economical on fuel than their petrol counterparts, generally go further on a tank of fuel and are quicker to refuel than pure electric models. 

A diesel model is also a good choice if you want a good tow car with plenty of oomph for pulling a caravan or trailer.  

However, many diesel models are less dependable than their alternatively fuelled siblings. In fact, diesels are the most problem-prone fuel type, with a fault rate of 31%. Pure electric models aren't far behind: 27 % those reported on had a problem. In contrast, petrol cars are more robust, with a fault rate of 20%, while hybrids are best of all with just 17% of plug-in hybrids (PHEVs) and 18% of regular hybrids going wrong.

Diesel models are also the least likely to be fixed for free; manufacturers covered the cost of only 67% of repairs for cars of this type, and 6% of owners paid out more than £1500 in repair bills. In contrast, 91% of hybrid owners had their cars fixed gratis, and only 2% of them had to find more than £1500 to cover fixes.

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Most reliable diesel cars

1. Renault Kadjar (2015-2022)

Reliability rating 98.6%

• Most common faults: non-engine electrics 6%, suspension 6%

• Average repair cost: £0

• Typical time off road: one day or less

The Renault Kadjar shares a lot of its underpinnings with the popular second-generation Nissan Qashqai, and that's a good thing because it's roomy and comfortable, and has a bigger boot than its Nissan sibling. As well as a range of quiet petrol engines, it comes with a pair of diesel engines that are frugal and have low emissions. 

Not only is the Kadjar the third highest rated family SUV for reliability, it's also the best diesel model in this class. Just 12% of the diesel Renault Kadjar models in our survey had a glitch, and the only areas to cause headaches were the suspension and various non-engine electrical systems. All issues were minor, though, and were rectified in a day or less by dealer service departments. Even better, the car maker covered the cost of all remedial work. 

Used Renault Kadjar review

2. BMW 3 Series (2012-2019)

Reliability rating 96.5%

• Most common faults: 12-volt battery 4%, bodywork 4%, suspension 4%

• Average repair cost: 50% £0, 50% £101-£200

• Typical time off road: one day or less

A superb all-rounder, the previous generation BMW 3 Series is one of the best secondhand executive cars you can buy. It's great to drive and has a well-appointed interior that's plusher and easier to use than those of many more expensive models. Although the engine line-up includes a range of petrols and a couple of hybrids, the vast majority of used 3 Series examples are diesels. That's no bad thing because they are all smooth and pretty punchy, and the cheapest 320d has an impressive official economy figure of 72.4mpg. 

The 3 Series is ageing well: only 15% of those we were told about had any problems, and all affected cars were fixed in a day or less by BMW dealers. While the car maker only covered the cost of 50% of repairs, the remaining bills wouldn't break the bank — no bills totalled more than £200.

Used BMW 3 Series review

3. BMW 3 Series (2019-present)

Reliability rating 96.0%

• Most common faults: engine electrics 10%, bodywork 3%, non-engine electrics 3%

• Average repair cost: 80% £0, 20% £1-£50

• Typical time off road: 20% one day or less, 60% a week or more

The latest 3 Series is a near-flawless executive car that's brilliant to drive and fitted with a great range of petrol, diesel and hybrid engines, and kitted out with the best infotainment system on the market. 

Diesel versions of the latest model are slightly more troublesome than their predecessors: 17% of cars went wrong, compared with 15% of previous 3 Series models. It's also more prone to problems than the petrol 3 Series, which has a fault rate of 9%. However, repair costs were minimal — BMW paid for 80% of fixes and the rest cost less than £50 per fault. The only downside is that 60% of cars were in the workshop for more than seven days. 

BMW 3 Series review

4. Skoda Kodiaq (2017-2024)

Reliability rating 94.7% 

• Most common faults: exhaust 6%, non-engine electrics 6%, air-con 2%, brakes 2%, engine 2%, interior trim 2%

• Average repair cost: 73% £0, 18% £301-£500

• Typical time off road: 46% one day or less, 18% more than a week

As well as being one of the most practical seven-seat SUVs you can buy, the Skoda Kodiaq is an affordable secondhand option. It has a roomy, classy interior and a punchy yet frugal 2.0-litre diesel engine. 

There's another benefit of choosing a diesel Kodiaq, too. Models with this engine have fewer faults than their petrol counterparts, according to owners, 20% went wrong compared with 22% of petrol models. Exhaust and electrical problems were the most common headaches, but most of these were fixed in a day or less. Although Skoda didn't cover the cost of all remedial work, it paid 73% of bills and only 18% of owners had to pay up to £500 to get their cars put right.  

Skoda Kodiaq review

5. Skoda Superb (2015-2024)

Reliability rating 92.9%

• Most common faults: engine 6%, suspension 6%

• Average repair cost: 67% £0, 33% £200-£350

• Typical time off road: 33% one day or less, 67% more than a week

If you want a family car with limousine-like levels of interior space, the Superb is well worth a look. Other plus points include a sumptuously appointed interior and low prices for secondhand examples. The 118bhp 1.6-litre and 148bhp 2.0-litre diesel versions dominated sales when new, and that means there are now plenty of used examples to choose from.

Another reason to choose a diesel Superb over a petrol model is its reliability record: only 13% of diesel cars went wrong compared with 35% of petrol models. Skoda and its dealers fixed two-thirds of cars for free, and the only annoyance for some owners is that many repairs took more than a week.  

Used Skoda Superb review

6. Volvo XC60 (2017-present)

Reliability rating 92.6%

• Most common faults: non-engine electrics 7%, sat-nav/infotainment system 7%, 12-volt battery 4%, bodywork 4%, brakes 4%, engine 4%, steering 4%

• Average repair cost: 67% £0, 33% £50-£350

• Typical time off road: 44% one day or less, 22% more than a week

You can't buy a diesel-engined Volvo XC60 new any more — it was discontinued in the UK in early 2024 — but it's well worth considering if you're after a luxurious secondhand family SUV. Feeling like a slightly shrunken version of the large Volvo XC90 SUV, the XC60 has a high driving position and oozes class inside and out. 

Diesel XC60 variants are marginally less likely to go wrong than their petrol or plug-in hybrid (PHEV) counterparts: 14% of diesels went wrong compared with 16% of petrol and PHEV models. Most are fixed in less than a week, and at no cost to owners, although some bills totalled up to £350. 

Volvo XC60 review

7. BMW X3 (2018-2024)

Reliability rating 92.4%

• Most common faults: engine  4%, engine electrics 4%, exhaust 4%, sat-nav/infotainment system 4%, air-con 3%, bodywork 3%

• Average repair cost: 78% £0, 6% more than £1500

• Typical time off road: 28% one day or less, 28% more than a week

Don't discount the 2018-2024 version of the BMW X3 because it has just been replaced, it's still one of the best large SUVs on the market. It has lashings of high tech kit, lots of interior space and a quiet, refined ride. It is a great value used buy, with prices broadly in line with the cost of a new BMW 1 Series family car.

Diesel and petrol X3 models both have a reasonable fault rate of 23%, although diesels have fewer sat-nav/infotainment issues than petrols. Diesels can be pricier than petrols to fix, though: BMW paid for 100% of petrol car fault repairs but only 78% of diesel bills. Petrols were quicker to fix too: 43% of faults were rectified in a day or less compared with 28% of diesel problems. 

BMW X3 review

8. Mercedes GLB (2019-present)

Reliability rating 92.3%

• Most common faults: non-engine electrics 18%, air-con 6%, interior trim 6%, sat-nav/infotainment 6%, bodywork 3%, engine electrics 3%

• Average repair cost: £0

• Typical time off road: 39% one day or less, 54% more than a week

The GLB is based on the B-Class MPV, but it's a practical seven-seater SUV that rivals the Land Rover Discovery Sport. It can carry lots of people or luggage, and our favourite version has a gusty 2.0-litre 220d diesel engine. 

Although 35% of the GLBs reported on in our survey had a problem, all issues were sorted out for free and 39% were put right in a day or less. All work was done for free by Mercedes and its dealers. 

Mercedes GLB review

9. Ford Focus (2018-present)

Reliability rating 89.7% 

• Most common faults: non-engine electrics 20%, battery 6%, brakes 6%, exhaust 6%, gearbox/clutch 6% 

• Average repair cost: 86% £0, 14% £351-£500

• Typical time off road: one day or less 14%, one day to a week 71%

Great to drive, practical and affordable to buy and run, the Ford Focus is an excellent family car. It's also one of the best driver’s cars in the class, with truly entertaining handling, especially if you go for ST-Line trim. As well as sharp dynamics, the Focus rides comfortably, is quiet on the move and is roomy inside. 

However, if you're after a Ford Focus you may be better off with a petrol rather than a diesel model. That's because 33% of diesels went wrong, compared with 9% of petrol models. Electrical niggles were the biggest bugbear, and 71% of cars were in the garage for up to a week. At least Ford covered the cost of most repair work, though. 

Ford Focus review

10. Mazda CX-5 (2017-present)

Reliability rating 88.5% 

• Most common faults: exhaust 11%, non-engine electrics 11%, bodywork 7%, brakes 7%, engine 7%, interior trim 7%

• Average repair cost: 71% £0, 7% £351-£750

• Typical time off road: 67% one day or less, 13% more than a week

The CX-5 is a five-seater family SUV that's small enough to tackle multi-storey car park with ease, and agile enough to make you smile on a country road. Although it doesn’t have a premium-brand badge on its nose, it’s well appointed and much cheaper than equivalent German-built alternatives.

Mazda generally has a strong reputation for building reliable cars, but the CX-5 bucks this trend with a fault rate of 48%. Although Mazda dealers fixed lots of issues swiftly, some took more than a week to put right. More worryingly, some owners had to find up to £750 to pay for their cars' fixes. 

Mazda CX-5 review

Least reliable diesel cars

1. Kia Sportage (2016-2021) 

Reliability rating 66.2%

• Most common faults: engine 24%, gearbox/clutch 20%, non-engine electrics 16%, brakes 8%, engine electrics 8%, bodywork 4%, exhaust 4%, fuel system 4%, sat-nav/infotainment system 4%

• Average repair cost: 83% £0, 9% £1000-more than £1500

• Typical time off road: 17% one day or less, 50% more than a week

The previous-generation Kia Sportage has been a mainstay of the Korean brand's line-up in the past few years, accounting for a quarter of all new car sales. Its popularity lies in the fact that it's attractively styled, practical, inexpensive to buy, and many secondhand examples will still be covered by some of Kia's comprehensive seven-year new car warranty.

However, this Sportage isn't living up to the usual high standard of Kia cars of dependability. Owners told us that 56% of their Sportages went wrong, many with engine and gearbox problems. More than half of the affected cars were out of action for more than a week, and some owners had to pay more than £1500 to get their cars fixed. 

Used Kia Sportage review

2. Volkswagen Golf (2020-present)

Reliability rating 70.4%

• Most common faults: non-engine electrics 11%, sat-nav/infotainment system 11%, air-con 8%, bodywork 8%, brakes 5%, engine 5%

• Average repair cost: 41% £0, 14% £1000-more than £1500

• Typical time off road: 41% one day or less, 33% more than a week

The Golf is unusual in that it's still offered new with the option of a diesel engine, offering high-mileage drivers an alternative to the petrol and PHEV versions. Whichever Golf you go for, you'll get a car that's good to drive, with a comfortable ride and a well-appointed interior.   

All Golf models have been troubled by a high proportion of problems in recent times, though. Although diesel Golf models have far fewer issues than their petrol or PHEV siblings, their fault rate of 30% isn't confidence inspiring. Petrol and PHEV Golfs have a fault rate of 45%.

Only 41% of problems were fixed for free by Volkswagen, leaving many owners with large bills: 14% of fault fixes cost at least £1000 per fault. Remedial work wasn't always swift either, with a third of faulty cars out of action for more than a week. 

Volkswagen Golf review

3. BMW 5 Series (2017-2023)

Reliability rating 79.8%

• Most common faults: exhaust 15%, engine electrics 9%, non-engine electrics 6%, 12-volt battery 6%, air-on 4%, bodywork 4%, sat-nav/infotainment system 4%

• Average repair cost: 46% £0, 35% £201-£750

• Typical time off road: 35% one day or less, 46% more than a week

The 5 Series is great to drive, comfortable and efficient, making it one of the best luxury cars you can buy. The 520d diesel 5 Series offers an excellent blend of performance and fuel economy. No wonder it's the best-selling version.

However, diesel versions of the 5 Series are far more prone to problems than petrol models: 43% of diesels had a problem, compared with 14% of petrol models. Owning a diesel 5 Series could be more costly, too, because BMW only covered the cost of 46% of repairs for faults on diesel cars, compared with 75% of those on petrol models. Finally, diesels were also slower to fix: 46% were out of action for more than a week, while only 25% of petrols took this long to fix.  

Used BMW 5 Series review

To read the reliability data for other car classes follow these links:

Most and least reliable cars overall 
Most reliable car brands 
Most reliable small cars 
Most reliable family cars 
Most reliable executive cars 
Most reliable luxury cars 
Most reliable small SUVs 
Most reliable family SUVs 
Most reliable large SUVs 
Most reliable seven-seaters
Most reliable electric cars 
Most reliable electric SUVs 
Most reliable sports cars 
Most reliable petrol cars 
Most reliable hybrid cars 

Reliability of diesel cars aged up to five years old

How the research was carried out

The annual What Car? Reliability Survey, conducted in association with MotorEasy, polls thousands of car owners about the reliability of their cars. The latest survey gained 29,967 responses and that enabled us to report on 199 models (up to five years old) from 31 different car brands. 

All car owners are asked to tell us if their car suffered any faults over the previous 24 months. For every car that has suffered a fault, we ask in what area the issue occurred, plus how much it cost to repair and how long it spent in the workshop. This information is used to create a reliability rating for each model and brand where we have a large enough response rate.

To gain a better insight into the areas that are causing problems, we also ask owners to let us know what part of the car was faulty. For all cars we have 14 different fault areas: air-con, battery, bodywork, brakes, engine or motor, engine or motor electrics, exhaust, fuel system, gearbox/clutch, interior trim, non-engine or motor electrics, sat-nav/infotainment, steering and suspension systems. On top of this, we've added two new categories for electric cars: charging and drive battery issues, and difficulties with electric motors.

About the report author

Claire Evans has been a motoring journalist for more than 30 years, working on consumer issues for a great deal of that time. After a stint as the advice columnist for Carweek magazine in the 1990s, she also spent six years working on motoring content for Which?. It is here she oversaw the running of the charity's annual used car reliability survey.

Claire launched the What Car? Reliability Survey in 2017, and since then has helped thousands of buyers choose the most reliable new cars and SUVs, as well as the most dependable used cars.

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