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 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 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.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC "Last Test Failed" clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

TEST DESCRIPTION

Steps 1-2:

The number below refers to the step number on 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.