P1621

Diagnostic Chart:

CIRCUIT DESCRIPTION
The control module Programmable Read Only Memory (PROM) contains data which is essential to the operation of the engine and the transmission. When the ignition is turned ON, the values in all of the PROM memory locations are added together and compared to a calibrated checksum number. If these two numbers are not equal, a DTC P1621 will be set. This test determines if any address locations have become corrupt.

CONDITIONS FOR RUNNING THE DTC
The engine is cranking or running

CONDITIONS FOR SETTING THE DTC
The VCM is unable to correctly read data from the EEPROM memory

ACTION TAKEN WHEN THE DTC SETS
^ The control module stores the DTC in history after the first failure but will not illuminate the Malfunction Indicator Lamp (MIL).
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
^ A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
^ Use the scan tool Clear Information function.

DIAGNOSTIC AIDS
Replace the VCM even if this DTC exists only in history. Refer to VCM Replacement/Programming.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Replace the VCM even if this DTC exists only in history.