Electronic systems have opened new opportunities for automating vehicle gearboxes, either partially or entirely. But an important condition - particularly for heavy trucks and buses - is that the equipment is highly reliable and has a long service life.A very high degree of automation can be achieved, and scope is available for controlling and coordinating the gearbox with the engine and other vehicle functions. Scania has chosen to automate the preselection of gears.The exact time at which the gear is engaged is left to the driver's discretion. The driver can use a small preselector lever, which is within easy reach, to override the computer and select a gear other than that the computer would engage. The automatically or manually preselected gear is actually engaged when the driver depresses the clutch pedal.The equipment for computerising the gear-shifting is designed for mounting directly on the existing five-speed and ten-speed Scania manual gearboxes.In addition to preselection and gearshifting functions, the Scania CAG system also includes economy, safety and fault-tracing functions.