BMW 320d
First common-rail diesel with unit injector technology. Solid basic design; weaknesses are the intake manifold (swirl flaps) and injectors at high mileage.
Economy diesel
Frugal yes, fun no. The engine keeps up with traffic, but every overtake needs a run-up.
Engine Weaknesses 7
The timing chain can stretch or the chain tensioner can fail. Compared to the N47 the M47 is considered more robust, but timing chain problems occur at high mileages and with neglected maintenance.
Symptoms: Rattling on cold start from the front of the engine, easing after warm-up. With heavy stretching, engine damage through chain jump.
The turbocharger can fail through oil feed line deposits or inadequate lubrication. Especially with infrequent oil changes or engine shutdown without cooldown.
Symptoms: Whistling noises, power loss, blue exhaust clouds, oil in intercooler.
The swirl flaps in the M47D20 intake manifold are secured with 2x M3 screws that work loose through engine vibration. Detached metal parts are sucked into the combustion chamber and cause total engine failure.
Symptoms: Delayed throttle response 1–2 seconds, rough idle, sudden engine damage through foreign body in combustion chamber
The exhaust gas recirculation valve carbons up over time and no longer opens/closes correctly. The coking accelerates especially with lots of short-trip/city driving.
Symptoms: Power loss, increased fuel consumption, rough idle, fault memory entry EGR.
From about 200,000 km the common rail injectors of the M47D20 wear and cause rough running and increased fuel consumption. Remanufactured injectors are considered unreliable.
Symptoms: Hesitation and rough idle, increased fuel consumption, poor starting behaviour, uneven injection quantity detectable on diagnosis.
The EGR valve of the M47D20 carbons up through soot deposits from the exhaust gas recirculation circuit. Power drops noticeably from 150,000 km. The intake manifold also carbons up.
Symptoms: Power loss at higher revs, jerky acceleration, increased soot emissions, EGR fault code
The O-rings of the common rail injectors of the M47D20 wear and allow fuel or exhaust gas to escape. Diesel smell in the cabin and starting problems are early warning signs.
Symptoms: Strong diesel smell with engine running at idle, rough cold start, oil-diesel mixture visible at injector holders
Vehicle Weaknesses 7
The plastic coolant expansion tank becomes brittle through thermal cycling and cracks or bursts — on almost every E46. A typical 3–4 cm crack appears along the housing edges. Risk of engine damage through overheating.
Rubber barrel bearings in the rear axle wear regularly. Repair requires full axle disassembly and special tools; Lemförder bearings recommended. Cost 400–630 € including wheel alignment.
The hydraulic bushings on the front control arms typically wear from 55,000 km. Wheel alignment is mandatory after replacement. Total cost 300–650 € depending on workshop.
The wheel arch liner wears through the primer at the inner wing seam. Rust grows from the inside and is only noticed once visible blisters appear. Welding repair is unavoidable.
The rubber O-rings in the VANOS unit become porous after around 100,000–165,000 km. The pistons then have excessive play, disrupting oil flow and camshaft timing.
The plastic sliders in the window regulator mechanism break almost universally. BMW doesn't supply sliders individually — only complete mechanisms. Cheap fix: aftermarket replacement sliders from third-party suppliers for a few euros.
Track rod ends wear as the joint grease dries out. Inexpensive replacement at around 100 € labour plus parts; always replace both sides and realign afterwards.