PCM EPROM Service

The PCM has an Erasable Programmable Read Only Memory (EPROM) computer chip that contains the calibration information used by the PCM to control fueling, idle speed, ignition timing, transaxle shifts, and vehicle emissions. The calibration information is based on various aspects of the vehicle, such as engine size, vehicle weight, transaxle type, final drive ratio, etc.

The EPROM must be programmed (flashed) with the correct calibration information that is critical to proper operation of the PCM (vehicle). Replacement PCMs used for service come without the programming, which must be performed by the technician, using the latest diagnostic tools and programs. In certain situations, the diagnosis and repair of the vehicle may require the technician to reprogram (flash) the PCM in order to eliminate a DTC or driveability concern. DO NOT interrupt the power supply to the PCM when performing EPROM programming. An interruption of power to the PCM while reprogramming the EPROM will cause the programming to be incomplete. Always use the latest service publications (bulletins, service manuals, etc.) for information concerning any new procedures on EPROM service.

The EPROM is soldered into the PCM and cannot be serviced separately.