PCM EPROM and EEPROM

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

Replacement PCM
Replacement PCMs 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 technical service bulletins be referenced for information concerning any new procedures or EPROM programs.

PCM Fails to Program
If the current program or an attempted reprogramming fails on the PCM, it will set DTC P0602, which is diagnosed in System Diagnosis / Procedures / Diagnostic Tables. Refer to the Service and Repair for information pertaining to PCM service procedures.

EEPROM

Important: Disconnecting the battery before the PCM is able to store the values may result in EEPROM reset, DTC P1526 and transaxle oil life and engine oil life being 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 TP Sensor learned value, Transaxle Shift Adapt values, and 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 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.

EEPROM Data Following PCM Replacement

Since the data contained in the EEPROM is specific to the vehicle that the PCM is in, the EEPROM should reset if the PCM is installed in another vehicle.

When this reset occurs, the following data will be erased:

^ TP sensor learn
^ Transaxle adapts (shifts, steady state, and garage shifts)
^ Transaxle oil life
^ Engine oil life
^ PCM odometer reading.

Resetting TP sensor learn will trigger DTC P1526. Resetting transaxle oil life will trigger the Change Trans Fluid message. Resetting engine oil life will trigger the Change Engine Oil Now message. The TP sensor learn can be relearned by following the DTC P1526 table. The transaxle oil life may be reset to its previous value using PCM transaxle oil life override. The engine oil life may be reset to 100 by displaying the Oil life left and pressing the Reset button. The transaxle adapts will be relearned during normal operation. The PCMs learned odometer reading must be reset with a scan tool on vehicles without a smart (serial data equipped) Instrument Panel (IP). Smart IPs communicate their odometer value to the PCM.