With night vision, adaptive cruise control, a sweet-sounding Harman Kardon audio system, and over-the-top features such as massage seats, the 2010 Mercedes-Benz S400 Hybrid is everything an S-class should be: one of the most comfortable cars on the road with a host of tech amenities. At the same time, it is also the least expensive S-class, both in initial price and running costs.
All of the cabin tech and driver assistance features in our test car are available across the S-class line, and we will get to those in a minute. First, however, we must discuss the novelty of an S-class hybrid.
Unlike the Lexus LS 600h, in which Lexus merely chose to add a big hybrid drive system to the LS' existing V-8, giving it tremendous power, Mercedes-Benz downsized the S-class engine, replacing the base level 5.5-liter V-8 with an Atkinson cycle 3.5-liter V-6.
A 20-horsepower electric motor assists that engine. The power doesn't sound like much, but the electric motor's more important function, assisting launches, benefits from its 118 pound-feet of torque, adding to the engine's 258 pound-feet. However, as a mild hybrid, this electric motor doesn't drive the car by itself; it merely boosts the engine.
Mercedes-Benz says that this combination gives the S400 Hybrid the power of a V-8, but that doesn't feel quite right. It is a big car, and it feels sluggish off the line. According to Mercedes-Benz's own figures, the S400 Hybrid gets to 60 mph in 7.2 seconds, whereas the V-8 S550 makes it in 5.4.
A button on the console toggles the throttle response between Comfort and Sport modes, the latter giving it a little more of a performance edge, but we found that it took a lot of gas pedal input to get anything like a quick take-off. The S400 Hybrid just doesn't move as effortlessly as the S550.
Mercedes-Benz kept the hybrid system's weight under control by using a 120-volt lithium ion battery pack--the first use of this type of battery chemistry in a major production hybrid. Because of the high power density, the battery is small enough that Mercedes-Benz packaged it under the hood, so it doesn't take up trunk or cabin space.
You can view the battery status from a graphic in the S400 Hybrid's speedometer, which shows the power flow from engine to battery to wheels. Likewise, the standard tachometer reveals this hybrid system's most useful feature: start-stop technology.
Stop the car at a light or in traffic, and the engine shuts down, saving gas. As soon as you lift off the brake, the engine kicks in again.
We found no problem with the functionality of this technology. For instance, the power was always ready when we wanted to go. But instead of a seamless push forward, we could feel the engine start up each time, which detracts a little from the car's overall luxury feel. However, this start-stop technology is easy to live with, and doesn't impinge nearly as much as in some other mild hybrids.
Although the driving feel isn't as good as we would have hoped, the hybrid system pays off in that the S400 Hybrid escapes the gas guzzler tax, which hits all of its siblings, and gets about 4 mpg better than the S550.
EPA gas mileage for the S400 Hybrid is 19 mpg city and 26 mpg highway. We achieved close to 21 mpg during our testing. As for emissions, the hybrid system gets it a Super Ultra Low Emission Vehicle rating from the California Air Resources Board.
A little sport
The faults we ascribe to this hybrid system show themselves only during urban driving; out on the open road, the S400 Hybrid feels no different from any other S-class. With the air suspension in Comfort mode, the car delivered an extremely smooth ride, insulating us from the outside world.
The big, plush seats contributed to the ride quality. With the Premium package, these seats incorporated massage technology, letting us choose between four different modes for the manner in which it would knead our backs. Mercedes-Benz includes dynamic seat bolstering with these seats, as well, which makes the bolsters inflate to counteract butt movement during cornering.
That latter technology might seem superfluous in a luxury cruiser like the S400 Hybrid, but this car offers some minor sport capability. Pressing the aforementioned throttle response button, we put the power train in Sport mode, and for good measure activated the Sport Suspension mode, using its separate button next to the LCD. The placement of these two Sport mode buttons, in very different places, is one of our minor annoyances with the car.