Circuit Description

EEPROM is a data storage unit which can save critical data even battery power is removed. This is used by the PCM to store TP sensor idle learned values, transaxle adapt values, transaxle oil life index and cruise control lash/learn.

The EEPROM has several locations available to store this information. If PCM detects a problem in one location of the EEPROM, it will store the data in another location. If PCM runs out of good locations in the EEPROM to store data, it will set the DTC.

The PCM stores the same data in its Keep Alive Memory so that even if the EEPROM is bad and DTC is set, the operator will not notice any difference in vehicle operation. Even after DTC sets, the PCM will continue to look for good locations in the EEPROM in which to store data and if it finds one, DTC will become a history code. EEPROM is soldered into the PCM and cannot be serviced. If a current DTC P1621 is set, PCM must be replaced.