2024 BMW M340i Problems: 10 Known Issues

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 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 2019-2025 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.