Premium German coupe with strong reputation for driving dynamics and build quality. Popular with business professionals and enthusiasts. Early models (2013-2014) use the improved N47N engine with relocated timing chain - far more reliable than pre-2011 N47. From 2015 onwards, the B47 engine brings even better reliability, fuel economy, and refinement. Main concerns: DPF and EGR issues on city-driven cars, timing chain on neglected examples, expensive AdBlue system failures, and ZF 8-speed transmission needs fluid changes despite BMW's "lifetime fill" claim. Diesel particulate filter lifespan is 250,000 km but regeneration problems emerge with short-trip driving patterns.
Carbon and soot accumulate, especially with short trips and city driving · more· less
The DPF requires temperatures above 550°C to burn off accumulated soot through regeneration. Short-distance and city vehicles cannot reach this temperature consistently, leading to blockages. Symptoms include DPF warning light, loss of power, black smoke, poor fuel economy, and increased fuel consumption. BMW states the DPF has a planned lifespan of 250,000 km. Chemical cleaning costs €350-600, while DPF replacement at BMW dealers runs €1,650-2,500 including labor. Prevention: drive at highway speeds (above 40 mph) for 30+ minutes at least once per week to allow proper regeneration.
EGR valve and cooler failure€450 - €1,800
Carbon buildup causes valve to stick, cooler can leak or crack causing intake manifold damage · more· less
BMW diesel engines from 2004-present are susceptible to EGR valve failure. The EGR valve becomes clogged with carbon deposits over time, leading to drivetrain warnings, lack of acceleration, sluggish performance, and no kickdown response. A recall affects 268,000 cars in the UK (produced August 2010 - January 2017) due to fire hazard - EGR cooler replacement may be free if your vehicle is covered. Standard replacement costs €250-450 at dealers, but if the EGR cooler cracks and melts the intake manifold, total repair can reach €1,800. Carbon buildup is worse on cars driven only short distances. BMW dealers may charge €177 for diagnostics before repair.
Chain tensioner loses pressure overnight, causes distinctive cold start rattle for 1-30 seconds · more· less
The N47N (2013+) and B47 (2015+) engines have significantly improved timing chain designs compared to pre-2011 N47 engines. However, the tensioner release valve can still weaken over time, allowing oil pressure to bleed off overnight. This results in cold start rattle typically appearing between 60,000-100,000 km. If rattle lasts more than a few seconds, the chain, guides, tensioner, and sprockets all need replacing (€1,000-2,200). BMW has updated the tensioner part. The B47 engine relocated the chain to the front for improved durability and easier servicing. Ignoring chain rattle can lead to chain skip and catastrophic valve/piston contact. Prevention: regular oil changes every 8,000-10,000 km with BMW-spec oil (5W-30 or 5W-40).
AdBlue system failure (NOx sensor, pump, heater)€500 - €2,500
NOx sensors degrade, DEF pump fails, system crystallizes, triggers limp mode and prevents starting · more· less
Common failures include NOx sensors (€300-400 each, two sensors total), DEF pump (€800+), AdBlue tank heater (fails in cold weather), and SCR catalyst degradation (worsened by poor-quality AdBlue). Wiring corrosion in DEF system connectors is also common. Full system repairs at dealers cost €1,500-2,500. Independent garages can repair crystallization issues for €250-275 by flushing lines. Symptoms include "AdBlue system malfunction" warning, limp mode with power loss, and eventual "vehicle will not restart" message. Using quality AdBlue from reputable sources helps prevent crystallization and sensor failures. B47 engines (2015-2019) are particularly affected by NOx sensor degradation.
Turbocharger failure or wastegate rattle€500 - €4,600
Actuator sticks from carbon buildup, turbo bearings fail from oil starvation, wastegate rattles · more· less
The turbo actuator tends to stick if the car is driven too gently or only for short trips, as carbon builds up. Symptoms include EPC light, limp mode, and loss of boost. Actuator-only repair costs €500-600 at specialists, but BMW dealers won't sell the actuator separately. Full turbo replacement runs €1,200-2,500 for parts, with total dealer costs reaching €4,000-4,600 including labor (approximately 16 hours). Wastegate rattle at certain RPM ranges is common and caused by failed wastegate vacuum lines or boost leaks. Prevention: change oil every 8,000-10,000 km (BMW's 15,000 km interval is too long), use premium fuel, and drive spiritedly occasionally to prevent carbon buildup. Battery must be healthy - low charge prevents coolant pump from cooling turbo after shutdown.
Water pump and thermostat failure€600 - €1,400
Electric water pump fails typically between 70,000-100,000 km, integrated with thermostat housing · more· less
The diesel engines use an electric water pump integrated with the thermostat housing. Failures are common between 70,000-100,000 km. Symptoms include coolant warning light, engine overheating, or poor cabin heating. The part costs €400-500 due to the integrated electric design, with labor adding €200-600 (approximately 6 hours due to accessibility). At BMW dealers, total cost runs €1,200-1,400. Independent shops using OEM-equivalent parts charge €600-800 total. Commonly, the electrical components inside the water pump fail first. Replacement is recommended every 60,000 miles preventatively to avoid being stranded. DIY costs around €380-450 in parts including thermostat and coolant.
Diesel injector failure€800 - €3,500
Carbon buildup on injector tips, wear from low-quality fuel, causes rough idling and misfires · more· less
Common diesel injector issues include carbon buildup on the injector tip leading to poor spray patterns and reduced fuel atomization. Symptoms include rough running, cylinders not firing properly, trouble starting, increased fuel consumption, and poor emissions. BMW offers two types of fuel injectors: budget versions around €200 and premium versions over €500 each. Dealer replacement of a single injector can cost €1,700+ including labor (Canadian pricing). Each injector must be coded per cylinder or running issues and possible damage will occur. BMW diesel engines have extended warranty coverage for injectors up to 150,000 km in some markets. If metal swarf is found during diagnosis, BMW may replace the entire fuel system. Prevention: use quality diesel fuel and fuel system cleaner additives.
Swirl flaps failure or sticking€160 - €2,200
Carbon and soot cause flaps to stick, or screws drop into engine causing catastrophic damage · more· less
Swirl flaps are butterfly valves in the inlet manifolds that improve low-speed fuel-to-air ratio. Over time, carbon buildup causes them to stick. The biggest risk is when affixing screws or the spindle break, dropping metal into the engine at 800+ rpm idle speed, causing catastrophic internal damage. If the intake manifold needs replacing, OEM BMW manifolds cost around €1,200, with labor bringing dealer totals to €2,200. Aftermarket manifolds cost under €300. Many owners opt for swirl flap delete/removal (€160-320) using aluminum blanking plates - this eliminates the failure risk with no perceived difference in performance or fuel consumption. The N47 and B47 4-cylinder diesel engines in the 420d are affected.
Rubber damper element perishes from oil contamination, pulley loosens, alternator belt snaps · more· less
The crankshaft pulley incorporates a rubber damper element that absorbs vibrations. Over time this can perish from oil contamination and fail. Common on B47 engines - one BMW specialist reports keeping them in stock now due to frequency. Reported failures as early as 38,000 miles. Warning signs include uncommon noise from engine bay, increasingly louder noise under acceleration, and excessive engine vibration. First symptom is often "battery not charging" message when the alternator belt comes off. BMW dealers quote €400-600 for the pulley alone, with total repairs reaching €1,200 at dealers. Independent mechanics charge €300-350 total using non-OEM parts. Some owners have received goodwill repairs from BMW. Replacement takes approximately 1-1.5 hours. If it breaks completely, it can damage much more than just the pulley - immediate replacement recommended when symptoms appear.
Harsh cold shifts, jerky behavior, sensitivity to fluid level despite BMW's "lifetime fill" claim · more· less
The ZF 8HP transmission is generally robust but experiences rough shifting when cold, harsh upshifts/downshifts in gears 1-2, firm engagements, and jerking between gears. Some owners report kangaroo-like behavior when cold. BMW claims "lifetime fill" (tested to 100,000 miles with acceptable failure rate), but ZF themselves recommend fluid service every 8 years or 50,000-75,000 miles. The transmission is very sensitive to fluid level - must be checked at precise temperature (30-40°C) and filled according to instructions. Fluid change costs €400-600 at specialists, using specific ZF fluid plus filter. Dealers may charge more. Regular service at 60,000-70,000 miles significantly improves shift quality and longevity. No widespread catastrophic failures reported - mostly comfort issues.
Suspension bushings and control arms€200 - €800
Rubber bushings degrade over time, causing clunking noises, vibrations, and poor handling · more· less
Factory rubber bushings wear from constant movement, heat, and road debris. Symptoms include increased body roll during cornering, excessive vibration and noise over bumps, clunking or shaking noises, cabin vibration, less precise steering feel, and uneven tire wear. Control arm bushings fail causing sloppy steering and poor handling. Front strut bushings wear causing rattling when the suspension components move without proper cushion. As bushings age, they become brittle, harden, shrink, and allow excess play in suspension joints. Replacement costs vary: individual bushings €50-150 each, control arms with bushings €200-400 per side, labor adds €150-400 depending on components replaced. Polyurethane upgrade bushings (Powerflex) offer improved durability and handling, with lifetime warranties available.
Above-average reliability for a diesel, but emissions systems need attention
The F32 420d is generally reliable when properly maintained, especially B47-equipped models from 2015 onwards. The main reliability concerns center around diesel emissions equipment (DPF, EGR, AdBlue) rather than core mechanical components. Cars driven primarily in city traffic will experience more DPF and EGR problems. Regular highway driving, proper oil change intervals (every 8,000-10,000 km rather than BMW's 15,000+ km recommendation), and using quality fuel significantly extend component life. The ZF 8-speed automatic is excellent but benefits from fluid changes despite BMW's claims. Overall, expect higher maintenance costs than equivalent petrol models due to diesel emissions complexity.
Pre-Purchase Inspection Checklist
General checks
Service history
Complete BMW dealer or specialist service records essential. Verify oil changes at proper intervals (every 8,000-10,000 km maximum, not BMW's 15,000+ km recommendation).
Tires
Check tread depth (minimum 3mm), tire age (date codes - replace if over 6 years old), and uneven wear patterns indicating suspension issues.
Cold start
Must start engine completely cold. Listen for timing chain rattle in first 30 seconds - any rattle lasting more than 2-3 seconds indicates chain wear.
Body condition
Check for rust (uncommon on F32 but check wheel arches), accident damage, paint mismatch indicating repairs.
Test drive
Minimum 30 minutes including highway speeds to bring DPF and transmission to operating temperature. Test acceleration, braking, and handling.
Specific for this vehicle
DPF regeneration cycle and warning lights
Check for DPF warning light on dashboard. Ask owner about regeneration frequency - frequent regens indicate city-only driving or impending DPF failure. During test drive above 60 km/h, fan noise may indicate active regeneration (normal).
Cold start timing chain noise
Start engine completely cold and listen carefully for rattle from rear (N47) or front (B47) of engine in first 30 seconds. Any persistent rattle beyond 2-3 seconds indicates chain tensioner or chain stretch. This is the most critical check.
EGR valve and turbo operation
During test drive, watch for EPC warning light, lack of acceleration, or hesitation. Test full-throttle acceleration - turbo should provide strong, smooth boost without smoke or lag. Black smoke indicates EGR/DPF problems.
AdBlue system status
Check dashboard for any AdBlue warnings. Verify AdBlue tank is topped up. Ask about any previous AdBlue system faults - these can be expensive and recurring. Check if NOx sensors have been replaced.
Automatic transmission shift quality
Drive for 15+ minutes to warm transmission. Feel for harsh shifts (especially gears 1-2), hesitation, jerking, or clunking. Some firmness when cold is normal, but should smooth out when warm. Ask if transmission fluid has ever been changed.
Engine oil level and condition
Check oil level on dipstick - should be between min and max marks. Check oil color and consistency - black is normal for diesel, but milky appearance indicates coolant contamination (head gasket or oil cooler failure).
Coolant system inspection
Check coolant level in expansion tank when cold. Look for leaks around water pump area, hoses, and radiator. White residue or staining indicates previous leaks. Listen for electric water pump operation when engine is running.
Suspension noises over bumps
Drive over speed bumps and rough road surfaces. Listen for clunking, rattling, or excessive noise from suspension. Check for play in steering wheel. Test corner handling - excessive body roll indicates worn bushings.
Brake operation and condition
Test braking from various speeds - should be smooth and straight with no pulsation or noise. Check brake pad thickness visually through wheel spokes. Ask when brakes were last serviced.
Check for recalls and TSB completion
Ask seller if EGR cooler recall (fire hazard, 2010-2017 production) has been completed. Verify with BMW using VIN. Check for any outstanding recalls or technical service bulletins.
Ownership pattern verification
Ask about typical journey types - short city trips are problematic for DPF and turbo. Ideal ownership history includes regular longer motorway journeys allowing DPF regeneration. Check annual mileage - very low mileage (under 10,000 km/year) on diesel raises concerns.
Recalls and Technical Service Bulletins
EGR cooler fire hazard (2010-2017 production)Verify completed
Crankshaft bearing shells (B58 engine July-Dec 2015)Not applicable to 420d
EPS steering motor mounting boltsExtended to 10 years/120,000 miles
Active Sound Design inoperative after programmingSoftware update available
Contact BMW with the vehicle's VIN to verify all recalls and technical service bulletins have been completed. The EGR cooler recall is particularly important as it addresses a fire hazard affecting 268,000 vehicles in the UK.
Warranty Status
Factory warranty (3 years/unlimited mileage)Expired on all F32 models
BMW Insured Warranty (UK/Europe)€500-1,000/year
Diesel injector extended warrantyUp to 150,000 km in some markets
All F32 420d models (2014-2020) are outside their original 3-year factory warranty. BMW Insured Warranty offers Comprehensive, Named Component, or DriveLine coverage options. Comprehensive Cover protects most components including wear and tear for the first 100,000 miles. Third-party extended warranties average around €500/year. Note that diesel emissions components (DPF, EGR, AdBlue) may have limited coverage under extended warranties - verify specific terms before purchasing.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.