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.
Since this diagnostic pertains to an internal VCM diagnostic check, no wiring schematic is required.
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 VCM records the operating conditions at the time the diagnostic fails. The VCM stores this information in the scan tools Freeze Frame and/or the 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 number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
|
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | ||
3 |
Does the scan tool indicate that this diagnostic Passed? | -- | ||
4 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
