Circuit Description
The powertrain control module (PCM) performs the checksum 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 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 random access memory (RAM). After retrieval, the PCM conducts a checksum 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, 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, this DTC 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 checksum that does not match previous checksum.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | 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 non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
If PCM power or 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.
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
2 | Is DTC P1621 also set? | Go to Step 4 | Go to Step 3 |
3 |
Does the scan tool indicate that DTC P0603 failed last test? | Go to Step 4 | Go to Intermittent Conditions |
4 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- |
