2012 Mercedes S400HV Hybrid Review

The current edition of the Mercedes-Benz S-Class flagship sedan made its appearance as a 2007 model, and underwent a mild nip and tuck facelift for 2010.

As part of the refresh, the German automaker also debuted its first gasoline-electric hybrid, the S400 Hybrid. As the world’s first mass-production automobile to employ a lithium-ion battery (the Tesla Roadster is a low-production vehicle), the S400 Hybrid is considered a milestone. And, rather than costing thousands more than its conventionally powered cousin, the S550, it costs thousands less. In fact, with a base price starting at $91,850, the S400 Hybrid is the least expensive S-Class model in the lineup.

Since its introduction as a 2010 model, the S400 Hybrid has not had any styling changes or revisions to features offered.

A Different Luxury Hybrid Approach

The Mercedes S-Class is renowned for its powerful engines; from the S550’s 429 horsepower V8 and culminating with the S65 AMG featuring the AMG-tuned V12 that produces an outrageous 621 horsepower. But instead of adding electric power to boost the output of a V8, the decision was made to offer a hybrid that would appeal to a more discerning driver: one that seeks a more eco-conscious way of traveling in luxury.

Developed jointly with BMW, the S400’s hybrid system is a “mild” hybrid similar to Honda’s Integrated Motor Assist hybrid powertrain, meaning it cannot be driven on electrical power alone. The 275 horsepower V6 gasoline engine is similar to the 3.5 liter used in other Mercedes cars and SUVs, but this version has different cylinder heads and pistons and a modified camshaft. It also uses a more efficient combustion strategy known as the Atkinson cycle, a common hybrid approach. The downside of the Atkinson cycle is diminished engine torque, especially at low rpm.

That’s where the electric motor comes in – think of its as sort of a substitute for a turbocharger that instead of cramming more fuel in, effectively reduces fuel requirements, while still yielding more total power. The small, disc-shaped three-phase external-rotor AC motor fits in the torque converter housing between the engine and the specially adapted seven-speed automatic transmission. When called upon, it adds 118 pounds-feet of torque and 20 horsepower to the V6’s output to boost starting acceleration and improve passing performance. The combined system generates 295 horsepower and an impressive 284 pounds-feet of torque. The compact motor also functions as a starter and generator.

Energizing the motor is a 32-cell, 120-volt, 0.9 amp-hour, lithium-ion battery. About the size of a shoebox, the battery fits neatly in the rear right-hand corner of the engine bay. Regenerative braking pushes electricity back into the battery.

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Like most hybrids, the Mercedes S400 system incorporates a stop-start function. When the car stops at a light or in traffic, the engine shuts off, saving fuel. Lift off the brake pedal and the engine instantly revives, briskly accelerating courtesy of the electric motor. In total, the hybrid system works with the German precision you would expect.

In the U.S. hybrids are about fuel mileage, in Europe it’s about emissions. The S400 Hybrid has an EPA estimated fuel economy of 19 miles per gallon in the city and 25 on the highway, for an average of 21 mpg – a little more than a 20 percent improvement over the S550. As for emissions, it has an extremely low CO2 output of 186 grams per kilometer and receives a Super Ultra Low Emission Vehicle rating from the California Air Resources Board.

Big European Sedan Style

Luxury rivals Audi, BMW, Jaguar and Lexus offer standard and extended wheelbase sedan models. For U.S. buyers, the S-Class comes only in one version, and it’s long – slightly more than 17-feet long. A deft pen, however, stretches out a well-proportioned body to create a low and lengthy body.

The hood points downward and merges into a pronounced arrow-shaped grille and wing-like headlamps. A steep windshield meets the roof that gracefully curves rearward towards a shallower raked rear window. Prominent wheel arches defeat the look of a big slab-sided car. The culmination of the design is a stately sedan with a big dose of European style.

Inside, there’s small doubt that the Mercedes S-Class has the most refined and luxurious cabin in the car business – Bentley and Rolls Royce excluded. Automobile Magazine summed it up with two words, “Gorgeous interior.”

Quilted leather highlighted by Eucalyptus wood trim dominates a supremely quiet cabin, with hardly an ounce of plastic to be found. Fit-and-finish is impeccable, and switches have a ribbed texture that operate with a substantial mechanical feel.

An option to seriously consider is massaging front seats, a pampering feature that Mercedes has perfected. Settings range from slow and light to fast and vigorous. Skip the upgraded seats and you’ll find the standard ones still impressive: 16-way power-adjustable, ventilated and heated.

The S400 Hybrid is brimming with interior tech starting with a 15-speaker harmon/kardon audio system, Bluetooth, ipod/MP3 interface, 7.2-GB music register and a hard-drive navigation system with Zagat. Optional is a dual-view navigation screen that can show a DVD movie to the front seat passenger and the navigation screen to the driver. The only electronic quirk is the COMAND interface that makes simple processes like tuning the radio or adjusting climate controls complicated and frustrating.

Driving Manners

We drove the S400h on the roads of Southern Germany. Our drive loop took us from Stuttgart – the home of Mercedes Benz – to the town of Buel and back, a round trip of approximately 150 miles. The route was evenly comprised of high-speed driving on the Autobahn – where we ran at, ahem, triple digit speeds – as well as moderately paced rural roads, and narrow streets through smaller hamlets.

Mercedes-Benz alludes to the S400h as having the power of a V8, but that’s a stretch. The company’s own numbers show the hybrid reaching 60 mph in 7.2 seconds compared with the V8 S550 making it in 5.4. That’s not say the S400 is a slug. Performance may not be exhilarating but the car felt surprisingly sprightly and right at home on the high-speed Autobahn.

The S400 drives much smaller than it is. Cutting through the tight twisties of Germany’s Black Forest, the hybrid cornered flatly and with confidence. It is as nimble and agile as its gas-powered counterpart. Stability comes from Active Body Control, a suspension system that continually adapts its tuning to the current driving situation. Other high-tech advancements include a pre-collision system, adaptive high beam assist, lane keep assist, and radar-based cruise control.

Of course, we tracked fuel economy and achieved an impressive 29.3 miles per gallon on our 150 mile jaunt – danged good for a car that weighs nearly 5,000 pounds. With much stricter speed limits in the U.S., it’s reasonable to assume fuel efficiency results will be even better.


To state the obvious, the S400 Hybrid is expensive. The base MSRP of $91,850 can easily and quickly climb from there when piling on the options. But for that price, not only are buyers getting the Mercedes-Benz prestige factor, they are also getting the engineering that the German automaker has built its reputation on. And for giving up a bit – just a bit – of performance, they are getting in exchange an S550 with better fuel economy and saving $2,600. That’s rather compelling for uncompromising affluent buyers seeking a slightly greener ride.

Prices are manufacturer suggested retail price (MSRP) at time of publication and do not include destination charges, taxes or licensing.

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