Bulletin
Engine code

IA Technical Bulletin

BMW B46 and B48 Engine Guide

Engine: B46

Bulletin text

IAIK means IA-insiders knowledge. Our collected BMW technical and ownership notes.

B46 and B48 · 1,998 cc · turbocharged inline-four, transverse and longitudinal installations · 2016-2020 US BMW models in the catalogue data, which ends with 12/2019 builds · X1, X2, 2 Series, 3 Series, 4 Series, 5 Series, Z4, X3, X4 and plug-in 3, 5 and 7 Series

B46 and B48 are BMW's 2.0 liter turbocharged four-cylinder engines, both listed at 1,998 cc. BMW's training says the B46 is based on the N20 and uses the same turbo, Valvetronic and direct-injection approach. That training covers it in one document with the three-cylinder B38 because the two engines are so similar. In BMW's engine designation the third character is 6 for the SULEV version of the turbo, Valvetronic and direct-injection design, and 8 for the turbo, Valvetronic and direct-injection design without the SULEV tag. That is the difference between B46 and B48. IAIK calls B46 the emissions-focused SULEV version of the family. IAIK adds that shared family architecture does not make transverse and longitudinal installations, or original and Technical Update engines, mechanically identical. BMW's B46TU and B48TU training gives 11/2018 as the start of production for both Technical Update engines.

Labels used in this guide: original means the first-generation engines, whose engine codes end in 0, such as B46A20M0. TU means the engines BMW's training calls B46TU and B48TU, listed as B46B20O1 and B48A20T1. BMW's repair data also lists other first-revision engines, with codes ending in 1, such as B46A20M1, B46A20O1 and B48B20M1. This guide does not say which Technical Update changes those other engines carry. Where a statement names only B46 or only B48, it applies to that code alone, and where it says both, it applies to both in the generation named. The BMW training we could read describes the original B46 in detail and the TU engines, but it does not describe the original B48 on its own, so statements about the original B48 rest on BMW's bulletins and catalogue data only.

Quick read

Ownership position: IAIK's position is to identify generation and installation before choosing cooling, belt-drive or ventilation parts.
Reliability: Not established as a rating. IAIK, from our own shop and one owner's G20 330i: a very solid engine, with no engine issues between 60,000 and 90,000 miles. BMW's own bulletins record specific service items, listed under Known Failure Points.
Cost to own: Not established by IAIK.
Power potential: BMW's training lists 231 hp for the original B46, 255 hp for the B46TU and 302 hp for the B48TU. IAIK gives no general tuned figure; one IAIK owner's tuned car is described under Power Potential.
Main watch item: Coolant leaks, starting with the oil filter housing and the cylinder head vent line.

Where you find it

This list is US-market BMW models from BMW's parts catalogue data, which ends with 12/2019 builds, so later years are not established here. Years are US model years, with build months at the cutover points.

B46, original generation

X1 sDrive28i and xDrive28i (F48): 2016-2019, built 07/2015 to 06/2019 (sDrive from 07/2016)
X2 sDrive28i and xDrive28i (F39): 2018-2019, built 11/2017 (xDrive) or 03/2018 (sDrive) to 06/2019
230i and 230i xDrive (F22 coupe, F23 convertible): 2017-2020, built 07/2016 to 12/2019
330i and 330i xDrive (F30 sedan): 2017-2019, built 07/2016 to 10/2018; 330i xDrive (F31 wagon): 2017-2019, built 07/2016 to 05/2019; 330i xDrive (F34 Gran Turismo): 2017-2019, built 07/2016 to 02/2019
430i and 430i xDrive (F32 coupe, F33 convertible, F36 Gran Coupe): 2017-2020, built 07/2016 to 12/2019
530i and 530i xDrive (G30): 2017-2019, built 11/2016 to 06/2019
X3 sDrive30i and xDrive30i (G01) and X4 xDrive30i (G02): 2018-2019, built 08/2017 (X3 xDrive) or 04/2018 to 07/2019

B46, later generation (catalogue label B46D, a first-revision code)

330i and 330i xDrive (G20 sedan) and Z4 sDrive30i (G29): 2019-2020, built 11/2018 to 12/2019
530i and 530i xDrive (G30): 2020, built 07/2019 to 12/2019
X1 sDrive28i and xDrive28i (F48 LCI) and X2 sDrive28i and xDrive28i (F39): 2020, built from 07/2019
X3 sDrive30i and xDrive30i (G01) and X4 xDrive30i (G02): 2020, built 08/2019 to 12/2019
228i xDrive Gran Coupe (F44): 2020, built 11/2019 to 12/2019

B48

X2 M35i (F39): 2019-2020, built 11/2018 to 12/2019, and M235i xDrive Gran Coupe (F44): 2020, built 11/2019 to 12/2019, both with BMW's catalogue label B48E
BMW's repair data ties the label B48E to the engine B48A20T1.

Plug-in hybrids

330e (F30): 2016-2019, built 11/2015 to 10/2018, catalogue label B48X
740e xDrive (G12): 2017-2019, built 07/2016 to 02/2019, catalogue label B48X
530e and 530e xDrive (G30): 2017-2020, built 03/2017 to 12/2019, catalogue label B46X

MINI Cooper S and John Cooper Works models use the same engine families and are outside this BMW guide.

B46 and B48 At a Glance

Question	Practical answer
Factory output	BMW's training lists 231 hp for the original B46A20M0, 255 hp for the B46TU and 302 hp for the B48TU.
Displacement and layout	1,998 cc, four cylinders in line, 82 mm bore, 94.6 mm stroke and four valves per cylinder.
Which generation is it	Read the last character of the engine code: 0 is an original engine and 1 is a first revision, and BMW's Technical Update engines are B46B20O1 and B48A20T1.
Transverse or longitudinal	BMW's training reads the fourth character of the code as A for transverse and B for longitudinal. In that training the X1 (B46A20M0) and X2 M35i (B48A20T1) are transverse, and the G20 330i and G29 Z4 (B46B20O1) are longitudinal.
Reliability profile	Not established by IAIK. The documented items are coolant leaks at the oil filter housing and the cylinder head vent line, a turbocharger oil return line gasket, the EVAP purge valve and, on early G20 and G29 cars, counterbalance shaft bearings.
Best ownership indicator	IAIK says to record the complete engine designation before planning a repair or build.
Typical annual planning budget	Not established by IAIK; the sources contain no cost figures.
Possible first-year catch-up	Not established by IAIK.
Largest common repair exposure	Not established by IAIK; the sources give no cost or frequency figures.
Common tuned street range	Not established by IAIK.
Upgraded-turbo range	Not established by IAIK.
Before buying or modifying	IAIK says to confirm the installed engine and generation before planning a repair or build. BMW's bulletins add VIN-specific checks for the vent line action, purge valve coverage and the counterbalance shaft recall, and an engine-code check for the oil filter housing bulletin.

Technical Specifications

Specification	Detail
Configuration	Four cylinders in line, turbocharged, with direct injection, double VANOS and Valvetronic. They are installed transversely or longitudinally depending on the model.
Displacement, bore and stroke	1,998 cc, 82 mm bore and 94.6 mm stroke on the original B46, B46TU and B48TU. The original B46 has 499.6 cc per cylinder and 91 mm between cylinders.
Engine code	BMW's eight-character code reads: BMW Group engine, cylinder count, basic concept (6 or 8), installation letter, displacement in tenths of a liter, performance class (M, O or T here) and revision (0 or 1).
Where the code is stamped	BMW's training places the 7-digit engine identification on the crankcase near the crankshaft alignment pin mounting, with the engine number embossed above it, and the seventh digit is the type-approval test number.
Block	The original B46 has an aluminum crankcase in a closed-deck, deep-skirt design with electric arc wire-sprayed cylinder running surfaces about 0.3 mm thick that cannot be machined afterward.
Cylinder head	The original B46 head is aluminum with cross-flow cooling, four valves per cylinder and a triple-layer spring steel gasket that BMW says must not be reused. BMW's TU training says the B46TU head has only slight modifications compared with the B46.
Crankshaft	Original B46: forged, with five main bearings and four counterweights. B46TU: revised, saving up to 1,043 g (2.3 lb). B48TU: reinforced, with a larger main bearing diameter.
Connecting rods and pistons	B46 and B46TU: drop-forged, cracked connecting rods with IROX-coated bearing shells on the rod side. Original B46: two compression rings and one oil scraper ring. B48TU: new pistons with modified compression and new rods without a small-end bearing.
Balance shafts	The original B46 has two counterbalance shafts turning at twice crankshaft speed.
Firing order	1-3-4-2, with a 180 degree firing interval (original B46).
Timing drive	The chain drive sits on the transmission side. Original B46: two-part chain with an intermediate shaft. B46TU and B48TU: one 8 mm sleeve-type chain, with 23 teeth on the crankshaft and 46 on the VANOS units.
Valvetrain	Valvetronic lift on the original B46 runs from 0.2 to 9.9 mm, and the eccentric shaft moves from minimum to maximum in under 300 ms.
Turbocharger	The original B46 has a twin-scroll turbocharger that keeps the exhaust from cylinders 1 and 4 and from 2 and 3 in two separate channels, with an electric wastegate. On the original B46, BMW's training says the exhaust manifold and turbocharger housing are one cast part that cannot be replaced individually. B46TU and B48TU: BMW's training says the turbocharger can be replaced individually and is all steel. B48TU: a larger turbocharger with an integrated air diverter valve.
Fuel system	Direct injection with the injectors bolted to a direct rail, so there are no high-pressure lines to the injectors on the original B46. Original B46: Bosch HDEV5.2 injectors and a maximum rail pressure of 200 bar. B46TU and B48TU: 350 bar (5,076 psi) injection pressure, with B46TU using HDEV6 injectors.
Cooling	Original B46: a mechanical coolant pump built with a map-controlled thermostat, a coolant-cooled turbocharger, and a 20 W electric pump that circulates coolant through the turbocharger after shutdown. B46TU: split cooling, with an electric valve on a heat management module that replaces the map thermostat.
Engine management	B46TU: DME8, in BMW's coding DME 8.4.0.
Engine oil	BMW's February 2017 oil chart lists 0W-20 with the Longlife-14 FE+ approval for B46 and B48 in its model year 2016 and newer table. That chart lists 5.25 liters (5.5 US quarts) for the B46 in the F48 X1 and the G30 5 Series, and for the B48 plug-in in the F30 and G12. BMW's repair data lists 5.25 liters with a filter change for original-revision B46 and B48 engines, and 5.25 or 5.75 liters for first-revision engines depending on market. The original B46 has no oil dipstick, and a sensor monitors the level electronically.
Oil filter	Original B46: an oil filter module with a built-in oil-to-coolant heat exchanger, and a filter bypass valve that opens at 2.5 bar.
Emissions	BMW's training reads the 6 in B46 as the SULEV version and says the original B46 met ULEV II when introduced.
Ignition	One ignition coil per cylinder, pushed into the cylinder head cover (original B46).

Named variants from BMW's training:

Variant	Installation	Output	Torque	Compression ratio	Note
B46A20M0 (original B46)	Transverse	231 hp at 4,700-6,000 rpm	350 Nm at 1,250 rpm	11:1	In use from 07/2014, model X1
B46B20O1 (B46TU)	Longitudinal (G20 330i, G29 Z4)	255 hp (190 kW) at 5,000-6,500 rpm	400 Nm (295 lb-ft) at 1,550-4,400 rpm	10.2:1	Start of production 11/2018
B48A20T1 (B48TU)	Transverse (X2 M35i)	302 hp (225 kW) at 5,000-6,250 rpm	450 Nm (332 lb-ft) at 1,750-4,500 rpm	9.5:1	Start of production 11/2018; BMW's table header prints this column as B48B20T1

IAIK's table lists the 302 hp engine as B48B20T1 and calls it a longitudinal TU. BMW's own model list names only the transverse X2 M35i, as B48A20T1, so this guide treats the longitudinal label as unproven. IAIK warns against identifying an X2 M35i from the B48B20T1 column just because the power figure looks similar.

The Insider Read

IAIK's rule is generation and installation first: original or Technical Update, transverse or longitudinal, before cooling, belt-drive or ventilation parts are chosen.

IAIK treats the shared family design as a starting point, not a parts swap. It says the Technical Update is not a reason to buy a mixed set of parts from several models, and that cylinder head details, cooling layout, belt routing and fuel-system parts need the matching generation and installation.

IAIK's ownership advice is diagnostic: find where the fluid is coming from before choosing a housing or a pump, and tell coolant from oil. It also says a closed-deck block is useful engineering context, not a tuning limit.

IAIK gives no general reliability rating, cost figure or tuned power range for these engines; the shop notes below are one shop's experience and one owner's car, not a rating.

What IAIK sees in our shop

The notes in this part come from IAIK's own shop experience and from one IAIK owner's car, not from BMW figures, and they are not failure rates.

IAIK rates the B46 as a very solid engine, and the owner behind IAIK drives one: a G20 330i. IAIK reports no engine issues on that car between 60,000 and 90,000 miles.

The only item on it was the tank vent (EVAP purge) valve, which IAIK had replaced at no charge under BMW's warranty extension, listed under Known Failure Points; it was not a recall.

IAIK hears many US owners call a 2019-2020 G20 330i a B48; IAIK points out that it is a B46, and BMW's catalogue data in Where you find it lists the 2019-2020 G20 330i under the B46.

Factory Deep Dive

Modular architecture, with an installation boundary

B46 and B48 belong to BMW's modular four-cylinder family. The original B46A20M0 in BMW's training has a closed-deck crankcase and electric arc wire-sprayed cylinder running surfaces. IAIK explains that the closed deck shuts the top of the coolant jacket around the cylinders and leaves defined coolant passages. IAIK adds that this describes block construction and does not establish a safe tuning limit.

Reading the engine code

BMW's bulletins often use a four-character short label instead of the full code. BMW's repair data ties B46O to B46A20O0 and B46B20O0, B46D to B46A20O1 and B46B20O1, and B48E to B48A20T1. BMW's own titles are not consistent: SIB 01 04 24 is titled G30 B48 but lists the 530i engine as B46O. Read the engine code on the block, not a bulletin title.

What the Technical Update changed (B46TU and B48TU)

B46TU: a modified cylinder head, a lighter crankshaft, a single-part timing chain, a modified belt guide, split cooling, a heat management module with an electric split cooling valve, 350 bar fuel injection pressure and DME8.
BMW says these changes cut CO2 emissions by 2.5 to 5 percent while adding 5 kW and 20 Nm (8 hp and 15 lb-ft).
B48TU: 302 hp and 450 Nm, a reinforced crankshaft with a larger main bearing diameter, new pistons with modified compression, new connecting rods without a small-end bearing, a larger turbocharger with an integrated air diverter valve, higher-flow injectors at 350 bar, new intake air pipes, a modified exhaust and an M Performance engine cover.
BMW's training lists the B46TU in the G20 330i and G29 Z4, and the B48TU in the X2 M35i.

Valvetronic changes from the N20 and N55 design (B46)

BMW's B46 training describes an assembled eccentric shaft, an adjustment range increased from 190 degrees (N20 and N55) to 253 degrees, and a smaller worm-gear ratio of 37:1. It also lists the omission of the separate worm-gear oil spray nozzle, and the worm gear now runs in an oil bath fed at the first eccentric-shaft bearing. IAIK says an N20 assembly checklist cannot simply be transferred to a B46, and that the absent nozzle is a design distinction, not evidence that Valvetronic lubrication is unnecessary. On the B46TU and B48TU, the VANOS units have 46-tooth camshaft sprockets in place of 36-tooth ones, and are shorter and more compact. BMW's repair data confirms a Valvetronic servomotor on both B46 and B48.

Crankcase ventilation changes path with load (B46)

BMW's B46 training describes a two-stage crankcase ventilation: under intake vacuum the blow-by gas is drawn into the intake ports, and under boost it goes into the clean air pipe ahead of the turbocharger. IAIK says the B46's cylinder head cover contains the ventilation passages and pressure-control hardware, with check-valve control keeping boost pressure out of the crankcase. IAIK adds that a damaged cover or a malfunctioning ventilation valve can affect more than an external oil leak, so the operating path matters when tracing oil carryover or abnormal crankcase pressure.

Cooling: original versus split cooling

On the B46TU, an electric split cooling valve can take the crankcase out of the coolant flow during warm-up and part load, so coolant runs through the cylinder head only, and BMW says the engine warms up faster and runs with lower emissions. A rotary valve inside the heat management module varies how far each coolant channel is open. On the B46TU and B48TU, the mechanical coolant pump has a pressure relief valve that opens above 2.2 bar (32 psi) and circulates coolant inside the pump until pressure falls, which BMW says helps the engine warm up sooner and reduces leaks and component damage from high pressure. The oil filter module holds an oil-to-coolant heat exchanger, the filter housing and the cover, and IAIK says oil and coolant passages meet there on the applicable installation.

Boost, fuel and oil supply

BMW's B46 training says no blow-off valve is used in the models it covers, and that pressure peaks are handled by engine software and wastegate control. The original B46 oil pump is map-controlled: the engine computer compares the oil pressure sensor reading with a stored map and adjusts the pump, and a second control loop holds oil pressure high if that control is lost. On the B46TU and B48TU, BMW's training says the maximum rail pressure is 350 bar, held across the operating range except at idle, where it drops to 150 bar. BMW's B46TU training says the HDEV6 injectors are hand-selected at the factory and tested for the least fuel leakage.

Technician service notes

Belt layout: BMW's B46TU and B48TU training shows one belt driving all the ancillary components, with an automatic tensioning pulley mounted on the alternator. The drawing is marked transverse, so it is not a routing diagram for every installation. BMW warns that incorrect belt installation can leave the coolant flow through the pump too low or absent, which risks engine damage. IAIK does not supply a universal mounting-bolt torque.

Cooling system refill (B46TU): BMW's training says the system needs a vacuum filler and the repair-instruction bleeding procedure after a part change or refill, and that filling from a can is not approved.

Fuel system and coils (original B46): BMW's training says the ignition coils are not fuel-resistant, so all coils come out before the fuel system is opened, and fuel residue is cleaned from the spark plug shafts before the coils go back.

Oil filter module (original B46, transverse installation): the housing is suspended, so the service is done from underneath, the two O-rings are replaced each time the cover or the drain plug is opened, and both are in the oil filter service kit.

Filler cap: BMW's training says to clean the oil filler neck before fitting the cap, because oil residue at the cap can lead to a wrong diagnosis of the crankcase ventilation.

Choose the repair after identifying the failed part: IAIK says a gasket repair needs a sound housing and mating surfaces, while a damaged housing needs the appropriate replacement assembly. It says to confirm the installed engine, housing revision, required seals and one-time-use fasteners in the vehicle-specific repair information, and not to infer bolt material, reuse rules or tightening values from another B-series installation. IAIK separates a documented defect or applicable service action from elective replacement of connected coolant hoses. IAIK treats an aftermarket metal housing as a product choice that needs exact fitment and quality evidence, not a factory requirement or a guarantee against future leaks.

Known Failure Points and Service Items

Recall information on this page was checked against NHTSA on October 1, 2026. Recalls are added and closed over time, and whether a specific car is covered is a VIN check with BMW or NHTSA.

01 Cooling leaks and the oil filter housing

IAIK says to locate the leak before choosing a housing or a pump: check coolant flanges, oil filter housings and coolant pump housings as they apply to the installed engine, and tell a coolant leak from an oil leak before building the parts list.

BMW's SIB 11 10 25, dated 2025-12-12, covers coolant leaking from the oil filter housing on G01, G02, G20, G22, G23, G26, G29, G30, G45 and G60 cars, but only those with the B46D, B48P or a plug-in hybrid four-cylinder engine. BMW says the housing seal can press too hard on the bushing (insert) in the housing, and the insert can deform and leak coolant externally. BMW's fix is new gaskets and a redesigned bushing. The bulletin lists no model years, and cars with the original B46O fall outside its engine restriction. See BMW SIB 11 10 25.

Watch for coolant loss and coolant residue around the oil filter housing. IAIK says fluid residue beneath the intake area does not identify the failed part by itself, and suggests keeping photographs of any pooling or staining with the inspection record. IAIK says heat exposure and loss of sealing compliance are useful inspection context, but they do not establish a fixed housing lifespan or a single failure mechanism for every B46 and B48 variant.

02 Cylinder head coolant vent line (SIB 17 01 21)

BMW's service action SIB 17 01 21 (revision 1, April 5, 2022) covers F22, F23, F30, F31, F32, F33, F34 and F36 vehicles produced April 24, 2015 to September 24, 2019. BMW says the quick-disconnect coupling on the cylinder head coolant vent line can break at the cylinder head and let coolant escape, because the line cannot cope with high temperatures over its life. The fix is to replace the cylinder head to expansion tank line, and the bulletin lists hose 17 12 9 845 173, or 17 12 5 A22 621 for plug-in hybrids. BMW says affected cars show the action as open in its systems, and its warranty defect code for the action reads F2x F3x B46 B48. It is a BMW North America bulletin that names only those eight chassis, so it does not settle other chassis or other markets. See BMW SIB 17 01 21.

Watch for coolant loss from the engine. IAIK says to check applicability by VIN before treating a vent-line complaint as a campaign repair, and to avoid disturbing an aged connection just to show that it can break.

03 Turbocharger oil return line (SI B11 15 17)

BMW's SI B11 15 17 (December 2017) covers oil leaking from the exhaust turbocharger oil return line where it meets the turbocharger, on F22, F23, F30, F31, F32, F33, F34, F36, G01, G12 and G30 models with B46O, B48M or B48O engines. BMW says the gasket was fitted flipped on affected cars, and the fix is a new oil return line, gasket and O-ring, with the gasket bead facing the oil return line. The bulletin lists chassis and engine codes, not model years. See BMW SI B11 15 17.

Watch for oil at the connection between the oil return line and the turbocharger.

04 EVAP purge (tank vent) valve

BMW extended the warranty on the EVAP system purge (vent) valve to 15 years or 150,000 miles from the original in-service date on listed vehicles, for defects in materials or workmanship. The bulletins and their listed vehicles are:

SIB 01 04 19 (revision 03, 2024-09-16): 2017 F22, F23, F30, F31, F32, F33, F34 and F36 cars (230i, 330i and 430i families) and 2016-2017 X1 sDrive28i and xDrive28i (F48), engine listed as B46O PZEV (SULEV).
SIB 01 02 24 (2024-05-01): 2018-2019 230i and 430i models, 2018 330i, 2018-2019 330i xDrive Sports Wagon, 2018-2019 X1 and X2 28i and the 2019 X2 M35i, with engine B46O except B48E for the M35i (the bulletin also lists six-cylinder B58M models).
SIB 01 04 24 (2024-10-07): 2017 530i and 530i xDrive (G30), engine B46O PZEV (SULEV).
SIB 01 03 24 (revision 01, 2024-09-12): 2019 X3 sDrive30i, 2018-2019 X3 xDrive30i, 2019 X4 xDrive30i and 2018-2019 530i and 530i xDrive (all B46O), and 2019 330i, 330i xDrive and Z4 sDrive30i (B46D).

BMW describes material and operational issues developing in the valve over time, which can cause hard starting, a rough-running engine (especially at idle), a metallic noise from inside the valve, stored fault codes and the check-engine light. BMW calls these notices of a warranty extension, not recalls or service actions, and says no repair is needed unless the car has the problem. BMW says to confirm coverage on the specific VIN, because its model lists are for information only. BMW's SIB 13 04 20 (revision 01, 2020-05-11) covers tank ventilation and mixture control faults stored in the engine computer on cars built up to March 2019 with B46X, B48X and other engine variants, and blames an internal mechanical defect in the tank ventilation valve, which can also make a loud clicking noise. See BMW SIB 01 02 24, SIB 01 03 24, SIB 01 04 19, SIB 01 04 24 and SIB 13 04 20.

IAIK's own G20 330i needed this valve, replaced at no charge under the warranty extension, and it was the only item on that car between 60,000 and 90,000 miles.

Watch for hard starting, a rough idle, a metallic ticking or clicking from the valve, and a check-engine light with mixture or tank ventilation faults.

05 Counterbalance shaft bearings on early G20 and G29 cars (recall 19V-732)

BMW recalled certain 2019-2020 330i and 330i xDrive and 2019 Z4 vehicles (NHTSA 19V-732) because the needle roller bearings of the counterbalance shafts may have been installed out of specification, which could loosen a shaft and cause severe engine damage. BMW's dealer bulletin (SIB 11 11 19, revision 1, 2019-11-08) names the G20 330i and 330i xDrive built November 20, 2018 to August 26, 2019 and the G29 Z4 sDrive30i built November 19, 2018 to April 3, 2019, with engine B46D. BMW's Part 573 report gives November 22, 2018 to August 26, 2019 for the 330i and May 24, 2018 to April 3, 2019 for the Z4, and 217 vehicles potentially involved. BMW's remedy is to replace the engine, free of charge. The recall notice itself does not name an engine code, and BMW's dealer bulletin names B46D. See NHTSA 19V-732 Part 573 report and BMW recall bulletin SIB 11 11 19.

Watch for a loud noise from the engine compartment on cars in those production windows, and check the VIN for an open campaign.

06 Misfire with compression loss

IAIK says a persistent misfire with compression loss needs mechanical diagnosis as well as fuel-system checks. IAIK explains that ring lands are the piston material between the ring grooves, and that damage there can weaken ring support and cylinder sealing, giving compression loss and blow-by. IAIK adds that these symptoms are not unique to a fractured ring land. It says to record misfire behavior, fuel-system findings and cylinder-sealing results before choosing a repair, and that a rail-pressure decay trace is supporting evidence, not a verdict on one injector. IAIK does not present this as a B46 or B48 production-wide defect and gives no failure rate.

Watch for a persistent misfire, low or uneven compression, and blow-by.

07 Crankshaft sensor recall (18V-465, several engines)

NHTSA recall 18V-465 covers certain 2018-2019 BMW and MINI models built from mid-May to mid-June 2018, and the BMW models it names include the X1 and X2 sDrive28i and xDrive28i, 230i, 330i, 330i xDrive, 430i Gran Coupe, 530i and 530e. BMW says a firmware error in the crankshaft sensor could stop it reading the crankshaft reluctor ring signal, and the engine could stall. BMW's remedy is to replace the crankshaft sensor, free of charge. The notice names models, not engine codes, and it also covers diesel and six-cylinder cars, so it is not specific to B46 or B48. See NHTSA 18V-465 Part 573 report.

BMW also issued MINI-only bulletins for B46 and B48 engines, for example SI M11 12 16 (September 2016), which covers MINI F55 and F56 built June 2014 to May 2015 and lists no BMW models, and those are not covered here. See BMW SI M11 12 16.

08 High-pressure fuel rail recall on 2022 cars (22V-513)

NHTSA recall 22V-513, reported July 20, 2022, covers certain 2022 X1 xDrive28i, X3 xDrive30i and 228i Gran Coupe vehicles. BMW says the high-pressure fuel rail may crack and leak fuel inside the engine compartment, which raises the risk of a fire. The notice names models, not engine codes; earlier model years of all three cars appear in the B46 lists above, and 2022 production is beyond the parts data used for those lists. Whether a given car is covered is a VIN check. See NHTSA recall listing, 2022 X3.

Reliability Verdict

Not established as a rating.

IAIK, from our own shop and one owner's G20 330i, rates the B46 as very solid: no engine issues between 60,000 and 90,000 miles, with the tank vent valve as the only item. That is IAIK experience with one car and one shop, not a failure rate.

The documents behind this guide record specific service items rather than one dominant failure: coolant leaks at the oil filter housing and the cylinder head vent line, a turbocharger oil return line gasket, the EVAP purge valve, and counterbalance shaft bearings on early G20 and G29 cars. None of these documents gives a failure rate across all B46 or B48 engines, a mileage or a service life, so this guide gives none.

Generation matters: the oil filter housing bulletin names B46D, B48P and plug-in engines, the counterbalance recall names B46D, and the oil return line bulletin names B46O, B48M and B48O. IAIK does not establish that every generation has the same failure pattern, or that a listed symptom proves one component is defective.

Power Potential

Not established as a general figure.

BMW's training lists factory output of 231 hp for the original B46A20M0, 255 hp for the B46TU and 302 hp for the B48TU. IAIK gives no general tuned figure. It says a closed-deck block is useful engineering context, but that build planning needs vehicle-specific fuel, cooling and calibration evidence, and that no universal horsepower ceiling is established.

IAIK, from one owner's car: the owner's G20 330i makes about 430 hp and 475-480 lb-ft on a custom tune, with the original turbocharger, untouched internals and no engine bolt-ons besides a catch can, and with maintenance done more often than normal. That is one IAIK owner's car on a custom tune, not a BMW figure and not a promise of what another engine will make or tolerate.

Cost of Ownership

Not established by IAIK. This guide gives no cost figures because none of its sources supports one.

One cost-relevant item is documented: BMW extended the EVAP purge valve warranty to 15 years or 150,000 miles on listed vehicles, and coverage is checked by VIN.