BMW 3 Series and X5 reliability by engine: petrol vs diesel vs PHEV fault rates 2026

© A. Krivonosov

One BMW had faults in just 6% of cars surveyed. Another, wearing the same badge on the same model line, had faults in 40%. A fresh What Car? breakdown shows that when buying a used BMW, the model name alone doesn’t tell the whole story: the petrol BMW 3 Series is markedly more dependable than its diesel and plug-in hybrid siblings, and the gap between powertrains on the X5 turned out to be almost threefold.

The survey, run by What Car? in association with MotorEasy, gathered responses from 29,967 owners. They reported on faults in cars up to five years old over the previous 24 months, along with repair costs and downtime. That means the final score reflects not just how often something breaks, but how much it hurts when it does. In total, 199 models from 31 brands were rated. BMW placed sixth among 30 brands with a score of 94.6%, ahead of Audi and Mercedes-Benz, which both scored 90.6%.

The top spot inside BMW’s own line-up went to the 4 Series Coupe and Convertible from the generation launched in 2021, at 98.5%. Only 8% of cars had any problems, mostly involving bodywork, steering and minor electrics. Every car stayed driveable, and repairs took no more than a week. By comparison, the previous 4 Series generation scored just 79%, underlining that it’s not only the model that matters, but the specific generation.

The petrol BMW 3 Series scored 98%. Faults were reported in 6% of surveyed cars. Diesel versions saw that figure climb to 27%, and plug-in hybrids to 26%. For the 330e, the main risk areas were the drive battery, engine electronics and gearbox, with some owners facing bills of more than £1,500.

A similar split turned up on the BMW X5. Petrol and plug-in hybrid versions scored 96.2%, with faults recorded in 14% of cars. Among diesel X5s, that rose to 40%, dragging the overall score down to 87.2%. Owners most often complained about the exhaust system, the engine, its electronics and bodywork.

This adds to an earlier SPEEDME comparison, where Consumer Reports data also showed BMW pulling ahead of Audi on reliability.that earlier comparison The new What Car? research is more valuable because it splits a single model by engine type: a brand’s strong overall result doesn’t guarantee equal reliability across petrol, diesel and hybrid variants.

The picture with electric cars is mixed. The older BMW i3 scored 97.4%, the i4 96.8%, and the iX3 95.5%. So an electric powertrain on its own doesn’t make a BMW troublesome. However, the larger iX came last in the brand’s ranking at 81%. A third of these cars had faults involving the battery, electric motor, infotainment, steering and charging system. Among the faulty examples, 62% couldn’t be driven, and 43% spent more than a week in the workshop.

The BMW iX1 finished second from bottom, at 86.8%. Its fault rate isn’t catastrophic — problems were reported in 19% of cars — but the weak points named include the infotainment system, the 12-volt battery, charging equipment and the electric motor.

For anyone buying a used BMW outside markets with full factory backing, the free-repair percentages from this UK survey carry limited practical weight. A long-running fault with a battery, drivetrain or infotainment system can mean sourcing diagnostic equipment and parts out of pocket rather than a free dealer visit — something worth factoring in wherever full manufacturer support isn’t guaranteed.

The ranking also shouldn’t be applied to every BMW generation. The data covers specific models up to five years old, and the next-generation X5 isn’t part of this sample. For the current car, the takeaway is clear enough: the petrol X5 looks like the safer bet over the diesel, and among 3 Series models, the lowest fault rate belongs to the standard petrol version.