P1621

CIRCUIT DESCRIPTION
The PCM checks the integrity of the non-volatile memory area of the Electrically Erasable Programmable Read Only Memory (EEPROM). The PCM uses the EEPROM to store information at key OFF. There are several locations within the non-volatile to store the information. If the PCM detects a problem in one location of the EEPROM, the PCM will attempt to store the data in another location. If the PCM runs out of valid places to store the information, DTC P1621 will set.

The PCM stores a copy of the previous key ON values in the non-volatile memory. When DTC P1621 sets, the PCM will default to the previously stored information. The vehicle operator will not notice a difference in operation. The PCM will continue to search for good non-volatile memory locations to store the information. A current DTC P1621 requires replacement of the PCM.

CONDITIONS FOR RUNNING THE DTC
The ignition is ON.

CONDITIONS FOR SETTING THE DTC
The PCM detects a malfunction in the non-volatile memory.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM will store the conditions present when the DTC set as Fail Records data only.

TEST DESCRIPTION

Steps 1 - 2:

The numbers below refer to the step numbers in the diagnostic table.
2. This vehicle uses a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.