It's safe to say a green revolution is sweeping the U.S., and it's even spread to the rarified air of the full-size luxury segment with the likes of the Lexus LS 600h L sedan. For 2010, that model is joined by the Mercedes-Benz S400 Hybrid, which achieves EPA-estimated gas mileage of 19/26 mpg city/highway. The hybrid gets 17 percent better mileage overall than the next-most-efficient S550, which is powered by a V-8 engine, but it comes with an unpleasant side effect.
The S400 Hybrid is technically a mild hybrid. This means that the electric motor between the V-6 gas engine and the seven-speed automatic transmission isn't capable of powering the sedan on its own. Instead, the hybrid system supplements the V-6's thrust when necessary, restarts the gas engine when pulling away from a stop (it shuts off to save fuel rather than idle) and doubles as a generator when braking to capture kinetic energy that'd otherwise be lost as heat.
The integration of the hybrid system is seamless in all respects except braking, where it lags other hybrids by a large margin in terms of pedal feel and progression. They have an early-stage, unfinished quality. No car at this price — hybrid or otherwise — should be so rough around the edges in terms of braking.
The 295-horsepower S400 Hybrid doesn't have the stupendous power of the 382-hp S550, which, until now, was the least powerful version of the S-Class available in the U.S. The hybrid, however, is quick enough, so there's no need to fret about having enough power to pull out into traffic. There's even a decent amount of reserve power on tap when cruising at highway speeds.
The S-Class is one of the most comfortable cars in the full-size luxury sedan segment and that trait lives on in the S400 Hybrid, which floats gently over the road courtesy of an air suspension. It's a setup that's ideally suited for long-distance drives and should help lessen driver fatigue.
The S400 Hybrid's cabin shouldn't tax the driver that much, either. It's a luxurious space with large, well-cushioned front bucket seats that have a multitude of adjustments and are available with an optional massage feature. There's no sacrificing the S-Class' impressive level of luxury — including its massive backseat — by choosing the hybrid model. The 16.4-cubic-foot trunk is essentially the same size as the gas-only model; the hybrid system's small lithium-ion battery pack fits in the engine compartment.
Besides being one of the few full-size luxury hybrids available in the U.S., the S400 Hybrid is notable for another reason. Hybrid versions of existing cars are typically near the top of the model's price range, but the S400 Hybrid is the least expensive version of the S-Class. With a starting price of $87,950, it's by no means cheap, but it's significantly less expensive than the performance-oriented LS 600h L's sticker of $108,800, and it's eligible for a $1,150 federal tax credit. I just wish the brakes were better.