Infiniti revived their use of the letter M in their alphanumeric branding scheme in 2003. Assigned to a coupe and convertible from 1990 to 1992, the 2003 Infiniti M45 was marketed as a high-end, four-door sport sedan. A distant, rear-wheel drive model, the M45's positioning in the Infiniti line-up was as a performance-oriented alternative to the Q45 sedan. In fact, the 2003 Infiniti M45's power came from the same VK45DE eight-cylinder engine. The 32-valve, 4.5-liter V-8 powerplant generated 340 horsepower and was connected to a five-speed automatic transmission. Heavily equipped with standard amenities, the first generation Infiniti M45 included HID headlights, heated mirrors, front and side airbags as well as a 225-watt Bose premium audio system was included. The introduction of a second generation M45 in 2006 with a new athletic appearance, the luxurious vehicle was available with Rear Active Steer. Solely offered as a rear-wheel drive sedan from 2003 to 2007, the 2008 Infiniti M45x provided all-wheel drive for the first time. The Infiniti M45 was dropped after the 2010 model year in favor of an upgraded M56 sedan.