The Mercedes-Benz S 400d 4MATIC, produced from 2020 to April 2023, represents a significant iteration of the W223 generation S-Class. Positioned as a diesel-powered offering within the flagship sedan lineup, it served as a compelling alternative to the gasoline-powered S 500 and the later S 580 models. The S 400d aimed to deliver a blend of luxurious comfort, strong performance, and improved fuel efficiency, appealing to buyers prioritizing long-distance cruising and refined driving dynamics. It utilized a sophisticated powertrain combination – a 2.9-liter inline-six diesel engine paired with a 9G-TRONIC nine-speed automatic transmission and Mercedes-Benz’s 4MATIC all-wheel-drive system – built upon the modular rear-wheel drive architecture (MRA) platform.
Powertrain & Engine Architecture
The heart of the S 400d is the OM 656.929, a 2.9-liter inline-six cylinder diesel engine. This engine is a cornerstone of Mercedes-Benz’s modern diesel strategy, representing a departure from the previous V6 diesel configurations. It features a sophisticated diesel commonrail fuel injection system, delivering fuel at extremely high pressures for optimized combustion. The engine employs a bi-turbocharger setup with a variable geometry turbine (VGT) and an additional turbocharger, enhancing both low-end torque and high-end power. The engine also incorporates an intercooler to further cool the intake air, increasing density and improving performance. The valvetrain utilizes a double overhead camshaft (DOHC) design with four valves per cylinder, optimizing gas flow and contributing to the engine’s efficiency. A key feature is the use of steel pistons, designed to withstand the high combustion pressures inherent in diesel engines. The engine also includes a particulate filter to minimize emissions, adhering to stringent Euro 6d-ISC-FCM emission standards.
The 9G-TRONIC nine-speed automatic transmission is a crucial component of the S 400d’s powertrain. This transmission is known for its smooth shifting characteristics and wide gear ratio spread, contributing to both fuel efficiency and responsive acceleration. It features a torque converter lockup clutch that engages across multiple gears, minimizing slippage and improving efficiency. The transmission is electronically controlled, adapting shift points based on driving conditions and driver input. The 4MATIC all-wheel-drive system operates with a rear-wheel bias, enhancing driving engagement while providing enhanced traction in adverse conditions. The system utilizes a multi-plate clutch to distribute torque between the front and rear axles as needed.
Engine Specifications
Key engine specifications include a compression ratio of 15.5:1, an engine oil capacity of 8.5 liters (8.98 US quarts), and a coolant capacity of 12 liters (12.68 US quarts). The engine also incorporates a Start & Stop system to further reduce fuel consumption and emissions during city driving.
Driving Characteristics
The S 400d delivers a distinctly different driving experience compared to its gasoline counterparts. While lacking the outright acceleration of the S 500 or S 580, it offers a substantial 700 Nm (516.29 lb-ft) of torque available from a low 1200 rpm. This abundant low-end torque provides effortless acceleration in everyday driving situations and makes overtaking at highway speeds remarkably easy. The 9G-TRONIC transmission is well-matched to the engine’s characteristics, providing smooth and seamless gear changes. The all-wheel-drive system enhances stability and traction, particularly in inclement weather. The S 400d achieves 0-100 km/h (0-62 mph) in 5.4 seconds, and 0-60 mph in approximately 5.1 seconds, demonstrating its respectable performance capabilities. The electronically limited top speed of 250 km/h (155.34 mph) ensures ample performance for most driving scenarios. The overall driving experience is characterized by refinement, quietness, and a sense of effortless power.
Equipment & Trim Levels
The S 400d 4MATIC typically came standard with a high level of equipment, befitting its flagship status. Standard features included Mercedes-Benz’s MBUX infotainment system with a large touchscreen display, a digital instrument cluster, leather upholstery, heated and ventilated front seats, a panoramic sunroof, and a premium sound system. Advanced driver-assistance systems, such as adaptive cruise control, lane-keeping assist, and automatic emergency braking, were also standard. Optional extras included a head-up display, massaging seats, rear-seat entertainment systems, and various interior trim options. The interior design emphasized luxury and comfort, with high-quality materials and meticulous attention to detail. Dashboard configurations were largely consistent across the W223 range, with variations primarily relating to trim materials and optional equipment.
Chassis & Braking
The S 400d utilizes an independent multi-link suspension system at both the front and rear axles, coupled with Mercedes-Benz’s AIRMATIC air suspension. This combination provides a remarkably comfortable ride, absorbing bumps and imperfections in the road surface effectively. The air suspension also allows for adjustable ride height, enhancing both comfort and practicality. The braking system features ventilated discs at all four wheels, providing ample stopping power. Anti-lock braking system (ABS) is standard, along with electronic brake-force distribution. The S-Class also incorporates 4-wheel steering (4WS), enhancing maneuverability at low speeds and stability at high speeds. The steering system is a rack and pinion type with electric power steering, providing precise and responsive steering feel.
Market Reception & Comparison
The S 400d was generally well-received by automotive critics, who praised its blend of performance, efficiency, and luxury. It was often highlighted as a compelling alternative to the gasoline-powered S-Class models, particularly for buyers who prioritize fuel economy and long-distance comfort. Compared to the S 500, the S 400d offered similar levels of luxury and technology but with lower running costs. The S 400d’s fuel consumption, ranging from 6.7 to 7.9 l/100 km (35.1 – 29.8 US mpg), was significantly better than that of the S 500. Reliability reports have generally been positive, with the OM 656 engine proving to be a robust and durable unit. However, as with any complex modern vehicle, potential owners should be aware of the costs associated with maintaining the advanced technology and systems found in the S-Class.
Technical Specifications
| Body type | Sedan, 4 Doors, 5 Seats |
| Fuel economy | 6.7-7.9 l/100 km (35.1 – 29.8 US mpg, 42.2 – 35.8 UK mpg, 14.9 – 12.7 km/l) |
| CO2 emissions | 175-209 g/km |
| Acceleration 0-100 km/h | 5.4 sec |
| Acceleration 0-62 mph | 5.4 sec |
| Acceleration 0-60 mph | 5.1 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 6D-ISC-FCM |
| Power | 330 Hp @ 3600-4200 rpm |
| Torque | 700 Nm @ 1200-3200 rpm (516.29 lb.-ft. @ 1200-3200 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | OM 656.929 |
| Engine displacement | 2925 cm3 (178.49 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Cylinder Bore | 82 mm (3.23 in.) |
| Piston Stroke | 92.4 mm (3.64 in.) |
| Compression ratio | 15.5:1 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | BiTurbo, Intercooler |
| Kerb Weight | 1995 kg (4398.22 lbs.) |
| Max. weight | 2770 kg (6106.8 lbs.) |
| Trunk (boot) space | 550 l (19.42 cu. ft.) |
| Fuel tank capacity | 65 l (17.17 US gal, 14.3 UK gal) |
| Length | 5179 mm (203.9 in.) |
| Width | 1921-1954 mm (75.63 – 76.93 in.) |
| Height | 1503 mm (59.17 in.) |
| Wheelbase | 3106 mm (122.28 in.) |
| Number of gears | 9 |
| Gearbox type | automatic transmission G-TRONIC |
Legacy
The S 400d 4MATIC, with its OM 656 engine, has established a reputation for reliability and durability. The engine’s robust construction and advanced technology contribute to its longevity. On the used car market, the S 400d represents a compelling value proposition, offering a significant amount of luxury and performance for the price. However, potential buyers should be diligent in verifying the vehicle’s maintenance history and ensuring that all scheduled services have been performed. The S 400d’s blend of refinement, efficiency, and performance ensures its continued appeal to discerning buyers seeking a luxurious and capable grand touring sedan.
