BMW 4 Series Service Costs

N20 (2.0 litre four-cylinder turbo) — pre-LCI — fitted to the 420i (135 kW / 184 hp) and 428i (180 kW / 245 hp) until 2016. The N20 carries the timing chain concern familiar from the F30 3 Series — the chain itself and particularly the chain guides can wear prematurely, with failure most commonly reported between 60,000 and 100,000 miles on cars with extended service intervals. Symptoms are typically a rattle on cold start that disappears once the engine warms up. We replace timing chain kits on these engines regularly and recommend shorter-than-CBS oil change intervals to prolong chain life.

N55 (3.0 litre inline-six turbo) — pre-LCI — fitted to the 435i (225 kW / 306 hp). The N55 is widely considered one of BMW's best modern petrol engines — strong performance, reasonable fuel economy for a six-cylinder turbo, and a generally good reliability record. Watch for valve cover gasket leaks (common on all N55s after 80,000 miles) and water pump failure around 80,000–100,000 miles. The N55 in the 435i is the connoisseur's choice for an F32 — strong torque, characterful sound, and a more involving drive than the four-cylinder variants.

B48 (2.0 litre four-cylinder turbo) — post-LCI — replaced the N20 from 2016 onwards. Fitted to the 420i (135 kW / 184 hp), 430i (185 kW / 252 hp), and other regional variants. The B48 is part of BMW's modular B-series family, designed from the start to address the failure modes of the N20 generation — different chain design, different oil pump architecture, generally more robust. From 2020 onwards (the final year of F32 production), B48-engined cars gained 48V mild-hybrid technology as standard.

B58 (3.0 litre inline-six turbo) — post-LCI — replaced the N55 from 2016 onwards in the 440i (240 kW / 326 hp). The B58 is widely regarded as one of the great modern BMW engines — strong performance, strong reliability record, and a smooth power delivery characteristic of BMW's inline-six tradition. The 440i is the most desirable non-M F32 variant on the used market.

N47 (2.0 litre four-cylinder common-rail) — pre-LCI — fitted to the 418d (105 kW), 420d (140 kW), and 425d (160 kW) until 2014. The N47 carries the well-known rear-mounted timing chain concern — failure typically requires engine removal to access the chain, making it one of the most expensive routine repairs on any modern BMW. We see N47 timing chain work regularly and can quote on this; we'd strongly recommend any F32 buyer have an N47 car inspected for chain stretch symptoms before purchase.

B47 (2.0 litre four-cylinder common-rail) — from 2014 — replaced the N47 in the 418d, 420d, and 425d, and continued through the LCI. Front-mounted timing chain (no N47-style rear-access issue). The B47 has a much better reliability track record than the engine it replaced and is generally considered one of the better modern BMW diesels.

N57 (3.0 litre inline-six common-rail) — pre-LCI — fitted to the 430d (190 kW) and 435d (230 kW, twin-turbo). The 435d xDrive in particular was a UK favourite — significant torque (630 Nm), strong real-world fuel economy on motorway runs, and a usable performance/economy compromise. The N57 carries the same general considerations as in the F30 — EGR cooler reliability, swirl flap considerations on early units, and DPF regeneration on cars used for predominantly short journeys.

B57 (3.0 litre inline-six common-rail) — post-LCI — replaced the N57 in the 430d and 435d from 2017 onwards. The B57 is the spiritual successor to the legendary M57 and N57 inline-six diesels and shares its architecture with the diesel engines in the G20, G30, and X5 ranges of the same era.

B48 (2.0 litre four-cylinder turbo) — multiple power outputs — the workhorse petrol engine of the G22 range. Fitted to the 420i (135 kW / 184 hp) and 430i (190 kW / 258 hp), plus the 420e plug-in hybrid variant (covered under Hybrid & Electric below). Same engine block as the G20 3 Series of the same era, different turbo and tuning. The B48 is widely regarded as one of the most reliable modern BMW engines, with a well-understood service profile after a decade in production. 48V mild-hybrid technology is standard across the range.

B58 (3.0 litre inline-six turbo) — fitted to the M440i (285 kW / 387 hp). The B58 carries over from the late F32 generation with revised tuning. The M440i is the highest-performance non-M G22 variant — strong real-world performance, an inline-six soundtrack that BMW has worked hard to preserve, and the closest analogue to the spirit of the old E92 335i for buyers who don't want or can't justify the full M4. 48V mild-hybrid as standard.

B47 (2.0 litre four-cylinder common-rail) — fitted to the 420d (140 kW). UK diesel demand has reduced significantly across the G22's production run compared to the F32 era — buyer preferences have shifted toward petrol and PHEV variants for company-car use, leaving the 420d as a smaller proportion of UK sales. Mechanically the B47 is the same well-proven unit as in the G20 320d, with the same maintenance profile and reliability record. Front-mounted timing chain. 48V mild-hybrid as standard.

B57 (3.0 litre inline-six common-rail) — fitted to the M440d (250 kW, twin-turbo, MHEV). UK availability of the M440d has varied across the production run; it remains a niche choice. The B57 carries the same maintenance profile as the equivalent G20 330d/M340d diesel.

420e plug-in hybrid (2021–) — B48 four-cylinder petrol engine combined with an electric motor. The 420e shares its drivetrain architecture with the G20 320e — 150 kW / 204 PS combined, 12 kWh battery (9.6 kWh usable), up to 60 km / 37 mi WLTP electric-only range. The 420e is the lowest-Benefit-in-Kind option in the 4 Series range and has been a strong company-car choice in the UK.

Service-relevant points for the 420e plug-in hybrid: the low-temperature cooling loop for the high-voltage battery and power electronics has its coolant level and condition checked at every service. The onboard charger benefits from periodic diagnostic interrogation, particularly on cars used for predominantly home AC charging. The 12V auxiliary battery works harder than on a pure ICE car (powering the BCM whenever the high-voltage system is dormant) and tends to need replacement earlier. We're fully equipped for plug-in hybrid servicing with isolation procedures and HV-rated tooling. The high-voltage battery itself is sealed and warrantied separately by BMW (typically 8 years / 100,000 miles).

48V mild-hybrid (MHEV) — standard on most variants — the 48V belt-driven starter-generator system fitted across most B48/B47/B57/B58 variants from launch provides smoother stop-start operation, brief torque assist during acceleration, and modest fuel-economy improvements. From a service standpoint the MHEV system adds two specific items: the 48V starter-generator belt is a longer-life part than a traditional auxiliary belt but does have a defined replacement interval, and the high-current 48V system requires isolation procedures during any work near the starter-generator or 48V battery. The 12V system runs in parallel as on a conventional car.

There is no fully electric (BEV) version of the G22 4 Series — BMW's electric mid-size offering is the i4, which despite the name shares its platform and most of its body with the G26 4 Series Gran Coupé rather than the saloon-bodied G20 3 Series.