The BMW 4 Series Convertible (G23) received a Life Cycle Impulse (LCI), or facelift, in March 2024. Among the updated variants is the 420d, a 2.0-liter four-cylinder diesel model producing 190 horsepower and incorporating mild hybrid technology. This version utilizes BMW’s Steptronic 8-speed automatic transmission and is positioned as a fuel-efficient, comfortable entry point into the 4 Series Convertible range, appealing to buyers prioritizing refinement and lower running costs over outright performance. The G23 LCI builds upon the foundation of the G23 platform, introduced in 2020, offering a blend of open-air driving enjoyment and modern BMW luxury.
Technical Specifications
| Brand | BMW |
| Model | 4 Series Convertible |
| Generation | 4 Series Convertible (G23 LCI, facelift 2024) |
| Type (Engine) | 420d (190 Hp) Mild Hybrid Steptronic |
| Start of production | March, 2024 |
| Powertrain Architecture | MHEV (Mild Hybrid Electric Vehicle) |
| Body type | Cabriolet |
| Seats | 4 |
| Doors | 2 |
| Combined fuel consumption (WLTP) | 5.2-5.8 l/100 km (45.2 – 40.6 US mpg, 54.3 – 48.7 UK mpg, 19.2 – 17.2 km/l) |
| CO2 emissions (WLTP) | 136-153 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 7.6 sec |
| Acceleration 0 – 62 mph | 7.6 sec |
| Acceleration 0 – 60 mph | 7.2 sec |
| Maximum speed | 236 km/h (146.64 mph) |
| Emission standard | Euro 6e |
| Weight-to-power ratio | 9.3 kg/Hp, 107 Hp/tonne |
| Weight-to-torque ratio | 4.4 kg/Nm, 225.4 Nm/tonne |
| Gross battery capacity | 0.4 kWh |
| Battery voltage | 48 V |
| Battery technology | Lithium-ion (Li-Ion) |
| Battery location | Under the front hood |
| Electric motor power | 11 Hp |
| Electric motor Torque | 25 Nm (18.44 lb.-ft.) |
| Electric motor location | Front, Longitudinal |
| Power | 190 Hp @ 4000 rpm |
| Torque | 400 Nm @ 1750-2500 rpm (295.02 lb.-ft. @ 1750-2500 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | B47 |
| Engine displacement | 1995 cm3 (121.74 cu. in.) |
| Number of cylinders | 4 |
| Engine configuration | Inline |
| Cylinder Bore | 84 mm (3.31 in.) |
| Piston Stroke | 90 mm (3.54 in.) |
| Compression ratio | 16.5:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Twin-power turbo, Intercooler |
| Valvetrain | DOHC |
| Engine oil capacity | 5.5 l (5.81 US qt | 4.84 UK qt) |
| Kerb Weight | 1775 kg (3913.21 lbs.) |
| Max. weight | 2260 kg (4982.45 lbs.) |
| Max load | 485 kg (1069.24 lbs.) |
| Trunk (boot) space – minimum | 300 l (10.59 cu. ft.) |
| Trunk (boot) space – maximum | 385 l (13.6 cu. ft.) |
| Fuel tank capacity | 59 l (15.59 US gal | 12.98 UK gal) |
| Permitted trailer load with brakes (12%) | 1600 kg (3527.4 lbs.) |
| Permitted trailer load without brakes | 750 kg (1653.47 lbs.) |
| Permitted towbar download | 75 kg (165.35 lbs.) |
| Length | 4768 mm (187.72 in.) |
| Width | 1852 mm (72.91 in.) |
| Width including mirrors | 2081 mm (81.93 in.) |
| Height | 1384 mm (54.49 in.) |
| Wheelbase | 2851 mm (112.24 in.) |
| Front track | 1573 mm (61.93 in.) |
| Rear (Back) track | 1612 mm (63.46 in.) |
| Front overhang | 858 mm (33.78 in.) |
| Rear overhang | 1059 mm (41.69 in.) |
| Ride height (ground clearance) | 124 mm (4.88 in.) |
| Drag coefficient (Cd) | 0.27 |
| Minimum turning circle (turning diameter) | 11.4 m (37.4 ft.) |
| Drivetrain Architecture | Rear wheel drive. MHEV. ICE and electric motor drive the rear wheels. |
| Number of gears and type of gearbox | 8 gears, automatic transmission Steptronic |
| Front suspension | Spring Strut, Transverse stabilizer |
| Rear suspension | Independent multi-link spring suspension with stabilizer |
| Front brakes | Ventilated discs |
| Rear brakes | Ventilated discs |
Powertrain & Engine Architecture
The 2024 BMW 420d Convertible utilizes the B47D20 2.0-liter inline-four cylinder diesel engine. This engine is a member of BMW’s modular engine family, known for its efficiency and refinement. The B47 features a common-rail direct fuel injection system operating at extremely high pressures (2,500 bar) for optimized combustion. A twin-scroll turbocharger with variable geometry turbine (VGT) technology minimizes turbo lag and enhances responsiveness across the rev range. The engine also incorporates an intercooler to further cool the intake air, increasing power output. The mild hybrid system, consisting of a 48V starter-generator, provides a power boost during acceleration and allows for smoother engine start/stop operation, contributing to improved fuel economy. The Steptronic 8-speed automatic transmission is a torque-converter type, offering smooth and quick gear changes. It’s programmed for comfort and efficiency in the 420d, with adaptive shift patterns based on driving style and road conditions.
Driving Characteristics
The 420d Convertible, with its 190 hp and 400 Nm (295 lb-ft) of torque, delivers a relaxed and refined driving experience. Acceleration from 0-60 mph takes approximately 7.2 seconds. While not a sports car, the engine provides ample torque for comfortable cruising and effortless overtaking. The Steptronic transmission is well-matched to the engine’s characteristics, providing smooth upshifts and downshifts. Compared to higher-output 4 Series variants like the M440i, the 420d prioritizes fuel efficiency and comfort over outright performance. The gear ratios are tuned for maximizing fuel economy, meaning the engine doesn’t rev as high or feel as urgent as in more powerful models. The mild hybrid system provides a subtle but noticeable boost during acceleration, filling in gaps in torque delivery.
Equipment & Trim Levels
The 420d Convertible typically comes standard with features such as BMW’s Live Cockpit Professional (digital instrument cluster and infotainment system), automatic climate control, leatherette upholstery, and parking sensors. Optional extras include premium leather upholstery, heated seats, a head-up display, and a premium sound system. The LCI update brought revised interior trim options and updated infotainment software. Specific trim packages, like Sport or Luxury, could be added to enhance the vehicle’s appearance and features.
Chassis & Braking
The G23 4 Series Convertible utilizes a sophisticated chassis design. The front suspension employs a spring strut setup with a transverse stabilizer, while the rear features a multi-link independent suspension, also with a stabilizer bar. This configuration provides a good balance between comfort and handling. The 420d typically features ventilated disc brakes on all four wheels, providing ample stopping power. ABS (Anti-lock Braking System) and electronic stability control are standard safety features.
Market Reception & Comparison
The 420d Convertible was generally well-received by automotive critics as a practical and efficient option within the 4 Series lineup. Its fuel economy (5.2-5.8 l/100km) is a significant advantage over the more powerful gasoline variants. Compared to the 430i, the 420d offers lower running costs but sacrifices some performance. The 420d’s diesel engine is known for its durability, but potential buyers should be aware of the higher maintenance costs associated with diesel particulate filters (DPFs) compared to gasoline engines.
Legacy
The B47 engine family has proven to be relatively reliable, although DPF issues can occur, particularly with frequent short trips. The 420d Convertible, as a more accessible entry point into the 4 Series range, has become a popular choice in the used car market. Its combination of style, comfort, and fuel efficiency continues to appeal to buyers seeking a premium open-top experience without the high running costs of more powerful alternatives. The mild hybrid technology introduced with the LCI update further enhances its appeal by improving fuel economy and reducing emissions.
