2021 BMW M340i Problems: 17 Known Issues

On the 2020-2021 BMW M340i, certain 2019-2021 BMW 3 Series (including M340i xDrive), X3 and X4 vehicles received driver and/or front passenger seat frames that the supplier did not weld to specification at the rail joint; affected 3 Series were produced between June 7, 2019 and April 12, 2021. An improperly welded frame may not restrain the occupant in a crash. BMW filed recall 23V-211 in March 2023 and mailed owner letters May 22, 2023. This is one of several G20 restraint recalls of the period: rear pretensioners 19V-912 affected the 330i, and front buckle sensors 20V-164 covered 2020 330i and M340i, among other models.

On the 2019-2022 BMW M340i, bMW SIB 65 23 23 and NHTSA campaign 23V-584 cover certain model-year 2019-2022 G20 M340i vehicles. Receiver Audio Module software may delay or fail to generate the audible driver seat-belt warning, causing noncompliance with FMVSS 208 and increasing injury risk if a driver relies on the reminder. Applicability is VIN-specific.

On the 2019-2022 BMW M340i, two software recalls hit the G20 M340i's rear-view camera under FMVSS 111. 19V-684 (Sept 2019, 257,473 BMW/Supra vehicles incl. 2019-2020 M340i) let the driver adjust the camera/display settings so that the rear image was no longer shown, and the car remembered the setting. 21V-096 (Feb 2021, 13,858 vehicles incl. 2019-2021 M340i/M340i xDrive) covered a fault where a portion of the rear image is obscured or the screen fails to illuminate when Reverse is selected. A third campaign in the same family, 22V-747 (Oct 2022), covers the 2023 330e only and does NOT list the M340i. Owners on Bimmerpost also report the iDrive 7 display going black for several seconds or the camera view failing to appear, which BMW treats with a PuMA software update.

On the 2021-2025 BMW M340i B58B30 (B58TU), from the 2021 model year the M340i added a 48V belt-driven starter-generator and 48V lithium battery alongside the conventional 12V starter. One recall targets the high-current connection on this car: 20V-761 (Dec 2020, 812 vehicles including 2021 M340i xDrive) for a 48V battery-to-starter-generator connection that may not have been assembled properly, raising resistance and fire risk. A later campaign for the same loose starter-generator connection, 25V-202 (Mar 2025), covers other B48-engined models (2025 330i, 530i, 4 Series, X3 30) and does NOT list the M340i. Separately, BMW ran a September 2024 service campaign for 48V batteries damaged in manufacturing, and owners report 'Battery cannot be charged / Do not continue driving', 'Starter generator malfunction' and '48V system malfunction' warnings, usually with auto start-stop disabled and the energy-flow display showing the 48V battery not charging. Dealers have quoted full starter-generator replacement for intermittent hot-restart faults.

On the 2019-2024 BMW M340i B58, m340i owners report the 12V AGM battery discharging or dying, sometimes on relatively young cars, often triggered by short-trip driving, parasitic drains from modules not entering sleep mode, or a failing Intelligent Battery Sensor (IBS). German owners on motor-talk specifically flag early failures of the OEM Sebang battery. After any DIY battery swap, failing to register the new battery to the power-management system leads to undercharging and repeat failures, and can leave a black iDrive screen plus multiple warning messages after a disconnect.

On the 2019-2023 BMW M340i, a very common G20 electrical fault: one or both exterior mirrors stop folding or unfolding, stop adjusting, or lose power entirely. BMW SIB 51 13 18 attributes it to faulty electronics inside the exterior mirror creating a short on the LIN bus, which can also discolor or crack the mirror glass; the fault is often intermittent and can cascade into the driver's door switch cluster so that window and trunk-release buttons also stop responding. BMW revised the module and later changed the repair procedure to replace only the failed module, but Bimmerpost owners report repeat failures of the replacement, with some cars on their second or third mirror. Owners outside the 4yr/50k warranty have had partial goodwill coverage approved through BMW regional service.

On the 2021 BMW M340i B58B30 (B58TU), on B58 cars built between September 2020 and May 24, 2021 (MY2021 M340i/M340i xDrive, also G22 M440i, G30 540i, X5/X6/X7 40i), the belt pulley on the mechanical coolant pump can fracture. When it lets go the serpentine belt comes off the coolant pump and alternator, so the engine loses cooling and charging at once and the shed belt can be drawn into the front crank seal. BMW issued Service Action SIB 11 05 21 to replace the pump/pulley on affected VINs; Bimmerpost owners report the pulley 'exploding' with the dealer replacing belt, pump and related components, and note the campaign did not always show on BMW's public recall lookup because it was a service action rather than a safety recall.

On the 2020-2022 BMW M340i, certain G20 M340i vehicles are eligible for BMW's VIN- and production-bounded lower active air-flap warranty extension. An air-flap warning requires diagnosis; it does not establish a failed actuator or universal hardware defect.

On the 2020-2024 BMW M340i B58 3.0L Turbo I6, the B58 engine's high-pressure fuel pump can fail, though at lower rates than the older N54 engine. When the HPFP fails, fuel pressure drops below the minimum required for proper direct injection, causing long cranking, rough idle, misfires, and in severe cases, the engine stalling and entering limp mode. Failures are more common in cold weather when fuel demands are higher, and can be exacerbated by ethanol-blended fuels.

On the 2020-2024 BMW M340i B58 3.0L Turbo I6, as a direct-injection engine, the B58 in the M340i does not have fuel washing over the intake valves, leading to gradual carbon deposit buildup on the valve backs. Oil vapors from the crankcase ventilation system deposit carbon that restricts airflow and reduces performance. Symptoms typically become noticeable after 50,000-80,000 miles, with rough idle, reduced throttle response, and minor misfires. The M340i's higher boost pressures can accelerate carbon accumulation compared to non-M B58 applications.

On the 2020-2024 BMW M340i, the B58 engine has a documented tendency for the paper oil filter insert to break apart in the housing. On rare occasions during an oil service, the genuine BMW filter insert is difficult to remove or breaks apart, with the paper torn and the lower plastic section stuck in the oil filter housing (BMW SIB 11 01 20). Shredded filter material can deposit paper fragments in the oil filter housing and potentially circulate through the oil system. BMW's bulletin documents this with genuine BMW filters.

On the 2019-2025 BMW M340i B58, the rubber valve-cover gasket and the oil filter housing gasket on the B58 inline-six harden and crack from repeated heat cycling, allowing engine oil to seep out. It typically appears from roughly 60,000-100,000 miles. Leaking oil can drip onto hot exhaust components (burning smell) and pool in the spark-plug wells, eventually fouling coils/plugs and causing misfires if left unaddressed.

On the 2020-2024 BMW M340i B58 3.0L Turbo I6, the B58 engine's electronic wastegate actuator can develop play over time, producing a characteristic rattling or buzzing noise at idle and during deceleration. The wastegate flapper valve develops clearance within its housing, causing it to vibrate at certain RPMs. While often described as just an annoyance, a severely worn wastegate can lead to boost control issues, over-boost or under-boost conditions, and eventually check engine lights for boost deviation faults.

On the 2019-2023 BMW M340i, separate from the fracture recall, a large number of G20 M340i owners report a knocking, cracking, or creaking noise from the front axle at low speed over bumps and expansion joints, often felt through the steering wheel and worse in warm weather. Dealers commonly replace lower control arms, sway-bar links, dampers and strut top mounts before finding the cause. BMW's SIB 32 01 23 ('Cracking/creaking noise from front axle/steering system') attributes it to excessive breakaway torque in the tie-rod thrust bearing on cars with the ThyssenKrupp (TKPS) electric power steering gear, and calls for replacing one or both tie-rod assemblies (both on cars built to 04/2019). A subset of owners only got relief when the dealer replaced the electric steering gear itself.

On the 2019-2025 BMW M340i B58, owners report harsh or jerky shifts from the ZF 8-speed automatic, most noticeable on the 1-2 and 2-3 changes at low speed before the drivetrain is warmed up, and aggravated by Sport mode in cold stop-and-go traffic. The ZF 8HP is sensitive to fluid condition; degraded or low fluid worsens shift quality, and in more severe cases the mechatronic valve body/control unit develops faults causing erratic shifting and transmission warning lights.

On the 2019-2025 BMW M340i, g20 sedans with the moonroof develop a rattle, ticking, or cracking noise from the roof over rough pavement and in heat, which many M340i owners describe as the single most annoying flaw in an otherwise quiet cabin. BMW addressed it with two G20 service bulletins: SIB 54 15 19 (groaning over rough roads or during body flex, treated by applying BMW Lubricant M to the glass panel perimeter seal) and SIB 54 16 19 (clicking from the roller sunshade, treated by greasing the sunshade guide rails with RHF 1 sunroof grease); some dealers remove the glass to clean and re-lubricate the seals and rails. Multiple owners report the fix lasting only a few months before the noise returns, making it a recurring maintenance item rather than a permanent repair; a minority needed rail or panel replacement.

On the 2019-2025 BMW M340i, the M340i's standard M Sport brakes (blue four-piston front calipers, semi-metallic pads) squeal loudly at low speed and light pedal pressure, especially in stop-and-go traffic and after the pads heat-cycle. It is one of the most repeated complaints on G20 forums and continues from the F30 340i with the same caliper family. BMW's position is that it is a characteristic of the performance pad compound; the dealer measure (PuMA 52226124-01) removes all four sets of pads, deburrs the pad edges on the disc-bearing surface, cleans and lubricates the contact points and reinstalls them. Owners report the fix is temporary and the squeal returns within weeks to months; a change to a quieter aftermarket pad compound is the only lasting cure, at some cost to bite and fade resistance.