Circuit Description

EEPROM is a data storage unit which can save critical data even battery power is removed. This is used by 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 data in another location. If PCM runs out of good locations in EEPROM to store data, DTC will set.

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