PROM (Programmable Read Only Memory)

This is factory programmed information, including engine calibration data, transmission, vehicle weight, and rear axle ratio application. The PROM can be removed from the ECM. If battery voltage is removed, PROM information will be retained. The PROM is listed as a calibrator in the parts catalogs.

The ECM incorporates a "learning" process that can make corrections to its preprogrammed information on air/fuel ratio to improve driveability. The learning process must be renewed whenever the battery is disconnected from the vehicle. To begin the process, the vehicle must be at normal operating temperature. Then drive the vehicle under part throttle, moderate acceleration, and idle conditions until normal performance characteristics return.