P1621

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) checks the integrity of the non-volatile memory area of the Electrically Erasable Programmable Read-only Memory (EEPROM). The PCM uses the EEPROM in order to store the information at key OFF. There are several locations where the information is stored within the non-volatile memory. If the PCM detects a problem in 1 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, Diagnostic Trouble Code (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 in order 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 control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

TEST DESCRIPTION

Steps 1-2:

The number below refers to the step number 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.