The DiabloSport Marathon Module helps you get better fuel mileage by enabling your V8 engine to behave like a four-cylinder engine when cruising, while still allowing for full V8 power when you need it. Easy installation. Just plug into the OBDII port under the dash and drive. Compatible with GM vehicles built from 2005 to current that feature Active Fuel Management (AFM). Enables vehicles with AFM to drop cylinders in order to suit the driver's power requirements, while conserving fuel. Saves fuel by allowing vehicle to stay in 4-cylinder mode 80% of the time as opposed to only 35% from the factory.