The M166 is a range of inline-four engines produced by Mercedes-Benz from 1997 to 2005, before it was succeeded by the M266 engine from 2004.
The M166 is transversely mounted and features 2 valves per cylinder with multipoint injection.[1] The engine is used in W168 A-Class models that feature the 'sandwich concept', where the engine is mounted at a 59-degree angle just behind the front axle.[2] This allows for better weight distribution as well as increased safety, as the engine slides underneath the floorpan instead of into the cabin in the event of a head-on collision.[3]