P0603

CIRCUIT DESCRIPTION
The PCM performs the check sum test to monitor the integrity of the non-volatile information across 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 check sum then stores the value along with the information. At key ON, the PCM retrieves the information from the EEPROM and places it in RAM. After retrieval, the PCM conducts a check sum of the information in RAM and compares this value to the value stored in the EEPROM at the previous key OFF. If the checksums do not match, DTC P0603 will set. Also, during operation, the PCM maintains a check sum on a certain section of the RAM that contains critical information. If at any time this running check sum fails, DTC P0603 will set.

CONDITIONS FOR RUNNING THE DTC
^ DTC P0604 is not set.
^ The ignition is ON.

CONDITIONS FOR SETTING THE DTC
The PCM detects a calculated check sum that does not match previous check sum.

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.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS
If PCM power on ground is lost during vehicle operation or during key down, DTC P0603 will set. The PCM keeps a continuous check on the non-volatile memory. If the memory changes, a PCM memory reset occurs. An intermittent loss of power or ground to the PCM will cause a reset.

TEST DESCRIPTION

Steps 1 - 4: