EPROM Information

PCM EPROM

The PCM houses an EPROM (Electrically Programmable Read Only Memory) that contains the calibration information used by the PCM to control the following processes:

^ Fueling
^ Idle speed
^ Ignition timing
^ Transaxle shifts
^ Emissions

This calibration information is based on various aspects of the vehicle. The list below includes some of the aspects that affect the calibration information:

^ Engine size
^ Vehicle weight
^ Transaxle type
^ Final drive ratio

The EPROM is programmed (Flashed) with this critical information. Replacement PCM's used for service come without the programming, which must be performed by the technician using the latest diagnostic tools and programs. Additionally, in certain situations, the diagnosis may require the technician to reprogram (Flash) the PCM in an attempt to eliminate a DTC or condition. Therefore, it is crucial that the latest service publications (bulletins, service manuals, etc.) be referenced for information concerning any new procedures or EPROM programs.

If the current program or an attempted reprogramming fails on the PCM, it will set DTC P0602, which is diagnosed in this section. Refer to the DTC P1627 Control Module Long Term Memory Performance.

PCM EEPROM

Important: Disconnecting the battery before the PCM is able to store the values may result in an EEPROM reset. The EEPROM reset will create the following results:

^ DTC P1526
^ Transaxle oil life will reset to 0
^ Engine oil life will reset to 0

The PCM contains a data storage unit which can save critical data even when battery power is removed. This unit, the electrically erasable programmable read only memory (EEPROM) is used by the PCM to store the following information:

^ TP Sensor learned value
^ Transaxle Shift Adapt values
^ Transaxle Oil Life Index

These values are stored in the EEPROM during the first 30 seconds after the key is turned OFF. Therefore, you should wait at least 30 seconds after turning the key OFF before disconnecting the battery to allow these values to be stored in the EEPROM.

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