BMW 420i G22

This is the most well-documented B48 engine issue and is the subject of a 2026 class action lawsuit in the US covering B46, B48, and B58 engines. The oil filter housing is made of polycarbonate plastic and sits between the engine block and intake manifold. Repeated thermal cycling causes the housing to become brittle and crack, while the gasket between the housing and engine block hardens and shrinks over time. Failure typically occurs between 60,000 and 120,000 km. Early symptoms include minor oil seepage visible from below, oil smell on the engine, or in more serious cases, coolant mixing with oil (milky residue on the oil cap). If coolant enters the oil circuit, engine damage can follow quickly. Repair requires removing the intake manifold for access. Independent BMW specialists in Western Europe typically charge €400-700 for gasket replacement or €600-1,200 if the entire housing needs replacing. BMW dealers charge more, with quotes reaching €1,000-1,500. Upgraded aluminium aftermarket housings are available and recommended for cars that have already experienced this failure once.

BMW announced a global recall in late 2025 and early 2026 affecting approximately 575,000 vehicles worldwide, including all G22 4 Series models. A manufacturing defect in the starter motor's magnetic switch allows metal particles to accumulate from normal start cycles, eventually causing a short circuit. This can generate intense heat in the starter assembly, with the potential to ignite surrounding components and cause a vehicle fire, even when the car is parked and the engine is off. BMW and safety regulators have urged owners to park affected vehicles outdoors, away from structures, until the repair is completed. The recall remedy involves replacing the starter motor and in some cases the battery, entirely free of charge. On a used car, this is the single most important item to verify before purchase. Contact BMW with the VIN to confirm the recall has been completed. If the car is outside warranty and the recall somehow does not apply, a starter motor replacement costs approximately €400-500 at an independent specialist.

The B48 engine uses a small rigid plastic coolant vent line that runs from the top of the cylinder head to the coolant expansion tank, positioned very close to the turbocharger. The proximity to turbo heat causes this plastic tube to become increasingly brittle over time and mileage. BMW issued a Technical Service Bulletin (SIB 17 01 21) in February 2022 acknowledging this issue and offering a revised rubber replacement part. In some markets, this was covered as a free service action. The tube can crack gradually, causing slow coolant loss that may not trigger an immediate warning, or snap completely, leading to rapid coolant loss and potential overheating. Symptoms include slowly declining coolant level, white residue around the tube fittings, or a sudden coolant warning. The replacement part itself is inexpensive (under €50), but labour at a BMW dealer can push the total to €400-800 due to access complexity. Independent shops typically handle this for €200-400. Check whether the revised rubber part has already been fitted, as this is considered a one-time fix.

The B48 valve cover uses an integrated PCV (positive crankcase ventilation) system, which means the entire valve cover assembly is affected when the gasket fails. The gasket hardens and shrinks from repeated heat cycles, typically starting to seep oil around 80,000-120,000 km. Oil drips onto the engine and exhaust components, producing a burning oil smell that is often the first symptom noticed by owners. The valve cover gasket itself is an inexpensive part (approximately €30-50), but the repair is labour-intensive because the ignition coils, fuel injectors, and several electrical connectors must be disconnected, and many technicians remove the intake manifold for better access. BMW dealers typically charge €600-800 for this repair. Independent specialists charge €350-500. Many owners combine this repair with the oil filter housing gasket, as the two jobs share overlapping labour. If deferred too long, oil can damage the serpentine belt and other rubber components below.

The B48 uses an electric water pump that has been improved over earlier BMW designs but remains a known wear item. The pump is electronically controlled and can fail electrically (motor burnout) or mechanically (impeller degradation). Failure typically occurs between 100,000 and 150,000 km, though some owners report earlier issues. Symptoms include coolant temperature warnings, erratic temperature gauge behaviour, reduced cabin heating, or in worst cases, engine overheating. The part costs approximately €300-400, with several hours of labour required due to packaging constraints. Most specialists recommend replacing the thermostat at the same time, as the integrated electronic thermostat is another common failure point at similar mileage. Total repair cost including both components runs €500-800 at independent shops and €800-1,200 at BMW dealers.

Cars equipped with iDrive 8 (standard on G22 models from mid-2021 onwards) have experienced a range of software-related problems. Forum reports from Bimmerpost and BimmerFest document random screen reboots during driving, the central display going blank for 30-60 seconds before recovering, Bluetooth pairing failures after phone software updates, and Apple CarPlay or Android Auto connections dropping intermittently. The navigation screen occasionally loses traffic data while the instrument cluster continues to function normally. Most of these issues have been addressed through over-the-air software updates, and BMW dealers can apply the latest software version free of charge during warranty. Out of warranty, a dealer diagnostic session and software update costs approximately €150-300. While these glitches are annoying rather than dangerous, they are widely reported and affect day-to-day usability. Earlier G22 models (2020-mid 2021) with iDrive 7 are generally less affected by these software stability issues.

A commonly reported issue on G-platform BMWs including the G22. The folding mirror mechanism can fail due to moisture entering the mirror electronics module, causing a short circuit on the wiring. This often occurs after cold weather, car washes, or when the mirror encounters resistance from ice. The folding motor itself can also seize or burn out. Symptoms include one or both mirrors failing to fold or unfold on command, grinding noises from the mirror housing, or intermittent operation. The Footwell Module (FRM) detects an over-current fault when motor stiction increases. Replacement of a single mirror assembly with auto-dim and folding function costs approximately €400-700 at a BMW dealer, or €300-500 at an independent specialist. The module typically needs coding after replacement. Some owners report recurring failures, particularly in wet climates.

The G22 420i has a heavy electrical load from its iDrive system, driver assistance features, and the 48V mild-hybrid integration (on 2021+ models). The 12V AGM battery manages the vehicle's conventional electrical systems and is under significant stress, particularly on cars that make frequent short trips or sit unused for extended periods. Battery degradation is commonly reported between 4 and 6 years of age, or around 50,000-80,000 km. Unlike older BMWs where a simple swap was sufficient, the G22 requires the new battery to be registered and coded to the vehicle's intelligent charging system through BMW diagnostic software. Without this step, the charging algorithm will remain calibrated to the old battery, accelerating failure of the replacement. Independent BMW specialists charge €250-350 for supply and coding, while BMW dealers charge €400-500. A quality battery tender (such as CTEK MXS 5.0) is strongly recommended if the car is parked for more than a week at a time.