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, diagnostic trouble code (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 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. |
Test Description
The number below refers to the step number in the diagnostic table.
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- |
