BMW 420d
Modular four-cylinder diesel, successor to the N47. Timing chain now at the front of the engine — the N47's biggest problem is eliminated. EGR and DPF remain wear items.
Reliable Diesel
Modern four-cylinder diesel — frugal and long-lived, but not a driver's engine.
Engine Weaknesses 6
Early B47 engines (2014–2016) are prone to premature chain elongation. The tensioner can no longer compensate. Rattling on cold start is the typical warning sign before chain snap and engine damage.
Symptoms: Metallic rattling or clattering on cold start; subsides after warm-up; in advanced cases audible during driving; MIL may illuminate
Overheating and leaking EGR coolers can vaporise glycol and trigger self-ignition. BMW recalled affected vehicles. If coolant enters the combustion chamber, hydraulic lock and engine damage are possible.
Symptoms: Coolant level drops without visible leak; whitish smoke from exhaust; rough idle; MIL; limp mode; rarely smoke from engine bay
With frequent short-trip use the DPF never reaches sufficient regeneration temperature. Soot accumulation blocks the filter and the engine enters limp mode. Long-term, oil level rises due to fuel intrusion.
Symptoms: MIL with message 'Particulate filter fault'; severe power loss; increased fuel consumption; black exhaust smoke on cold start; oil level rising
Common-rail injectors operate at up to 2,500 bar and wear at higher mileages. Knocking noise on cold start and misfires on individual cylinders. Replacement is complex and expensive.
Symptoms: Knocking noise on cold start; fault code 'injection quantity out of tolerance' or 'cylinder X misfire'; stumbling; increased consumption
From about 150,000 km onwards, failures of the electronic thermostat and electric water pump become more frequent. Overheating without early warning is possible. Replacing both parts simultaneously is recommended.
Symptoms: Coolant temperature rises unusually quickly or too high; heater blows cold; fault codes relating to the water pump; rarely a sudden failure
Primarily urban short-trip use causes the EGR valve to coke up. Power loss and increased emissions.
Symptoms: Power loss, rough running, engine check light, black smoke
Vehicle Weaknesses 14
Official recall: moisture can enter the starter motor and cause corrosion. In extreme cases there is a fire risk.
The recall for moisture-induced starter corrosion also affects the G82 M4.
On early G22/G26 models, sporadic complete software failures: iDrive freezes, navigation fails.
On the M440i xDrive with 48V mild hybrid, the battery can become deeply discharged after short-distance driving.
After extended periods of inactivity, brake discs rust so heavily that the parking brake seizes and disc replacement becomes necessary.
After software updates, unwanted downshifts at 120 km/h to 7th gear. Sporadic electrical errors after service.
Climate control fails periodically around freezing point — compressor cycles off, the anti-mist sensor re-engages it.
M Sport suspension shock absorbers can gradually wear from around 75,000 km.
Standard M compound brake discs squeal at low speeds below 50 km/h. BMW classifies this as design-inherent.
On the G82 M4 xDrive, the tyre makes contact with the bumper cover at full lock.
On the G82 M4, annoying wind noise at the driver's door appears from around 130 km/h. Cause is a door seal or door frame gap not sitting flush; dealers resolved it through readjustment.
Front control arm rubber bushings develop creaking and clicking noises at low temperatures. BMW has provided replacement parts with a Teflon coating.
Many G82 owners report unusually large and deep stone chip damage even on new cars. The paint layer is thinner than on predecessor models; chips of 3–10 mm after a short period of use are normal.
On some G82 M4s, a metallic click occurs when shifting from reverse to neutral or downshifting to a stop. BMW service has replaced the park lock mechanism in documented cases.
Reports & Tests
2 owner complaints filed with NHTSA (2020–2026). Most reported: Other (2), Brakes (2), Collision Avoidance (1).