BMW 120d
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 7
EPS issues are widespread on the F20: the rack binds, aluminium bolts corrode on vehicles built July 2011–May 2015, and the electric motor can detach from the rack. Full replacement usually necessary.
The EGR valve and EGR cooler can fail or leak on N47 and B47 diesel engines. In the worst case, coolant ingress can cause engine fire.
Water enters through displaced cable grommets, faulty door seals, or blocked sunroof drains. Problem occurs across all F20 production years.
On N13 and N55 engines, valve cover gaskets go brittle and the crankcase ventilation fails. Oil consumption rises to 0.5–1 litre per 3,000 km.
Shaft seals on the rear differential leak gear oil. Problem often appears as early as 25,000–50,000 km, especially on M135i and M140i.
Clattering rear axle caused by worn shock absorbers, known from production date 04/2012 onward. Dampers are regularly flagged at MOT. Track rod ends also wear prematurely.
The 6-speed automatic shows jerky shifts or delayed response — typical between 50,000 and 100,000 km. Software update on the gearbox control unit often helps.