The S400 Hybrid is the gas-electric version of Mercedes-Benz's opulent S-Class full-size luxury sedan. It offers marginally better fuel economy than the eight-cylinder S550, although its efficiency numbers are significantly less impressive than those of the diesel-powered S350 BlueTEC 4MATIC.
A 3.5-liter V6 and an electric motor team up for a combined output of 295 horsepower and 284 pound-feet of torque. Fuel economy for the S400 is rated at 19 mpg in the city and 25 mpg on the highway.
The S400 Hybrid is the first series production hybrid car to be equipped with a lithium-ion battery. During braking the electric motor acts as a generator and is able to recover kinetic energy. The lithium battery is particularly suited to this task. The battery's high energy density means it is small enough to fit in the engine compartment. As such, the trunk capacity and interior dimensions remain unchanged. The car's 7G-TRONIC seven-speed automatic transmission is specially configured for hybrid operation.
As with other S-class models, the S400 Hybrid features a number of updates for the latest model year, inclyding addition of daytime LED running lights fitted to the outer edges of the bi-xenon lamp units. The rear end is also accented with a total of 52 distinctively arranged LEDs in the two taillights. Gone are the body-colored strips through the taillamps.
Mercedes-Benz also makes more use of light as a styling element in the interior via the standard ambient lighting, now with a choice between three lighting moods: solar (amber), neutral (white) and polar (ice-blue).
Another noticeable change at the front of the car is a more pronounced arrow-shaped grille, plus a new front bumper with a light-catching contour and a chrome strip below the cooling air intakes. Exhaust tailpipes of all S-Class variants are now visibly integrated into the rear bumper. Mercedes-Benz says its engineers have also implemented specific aerodynamic measures to reduce wind noise.
Camera and radar-based driver assistance systems include Adaptive Highbeam Assist, Lane Keeping Assist and the Pre-Safe brake system linked to the proximity regulating radar, which intervenes autonomously before an impending rear-end collision. Other highlights include the Attention Assist driver drowsiness monitor and Active Body Control with automatic crosswind stabilization.
Engineers also managed to improve the night-vision system with the introduction of Night View Assist PLUS, which is equipped a special pedestrian detection function. The Pre-Safe braking system has also been improved to reduce injuries in unavoidable crashes. Mercedes says the car can apply maximum braking pressure automatically around 0.6 seconds before what is recognized as an unavoidable accident. The system therefore acts as something like an "electronic crumple zone," Mercedes contends.
The multifunction steering wheel of the S-Class has been modified for improved aesthetics and feel. The rim and airbag module are now lined with soft premium leather as standard. The new, flatter airbag module also lends a sporty touch to the multifunction steering wheel.
Large luxury sedans and hybrid technology are a new match, but the S400 still has a few competitors, including the arch-rival BMW 7-Series ActiveHybrid, the Lexus LS 600h L and possibly the smaller Infiniti M Hybrid if size isn't as important as being green.