DTC P0603: Control Module Long Term Memory Reset: Description

Powertrain Control Module (PCM) performs the checksum test in order to monitor integrity of the non-volatile information across the ignition cycles. The PCM uses an Electrically Erasable Programmable Read-Only Memory (EEPROM) to store this information at key off. Before storing the information, the PCM calculates a checksum then stores the value along with the information. At key on, the PCM retrieves the information from the EEPROM and places the information in the Random Access Memory (RAM). After retrieval, the PCM conducts a checksum of the information in RAM and compares this value to the value that is stored in the EEPROM at the previous key off. If the checksums do not match, Diagnostic Trouble Code (DTC) P0603 will set. Also, during operation, the PCM maintains a checksum on a certain section of the RAM that contains critical information. If at any time this running checksum fails, DTC P0603 will set.