P1621

DTC P1621 Control Module Long Term Memory Performance

Circuit Description
The Powertrain Control Module (PCM) is the control center of the fuel injection system. It constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (MIL) (Check Engine), and store a DTC or DTCs which identify the problem areas to aid the technician in making repairs.

Conditions for Setting the DTC
The PCM cannot communicate internally.

Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM will attempt to record the operating conditions at the time during which you detect this failure, however, since this is a internal PCM failure, you cannot rely on this information. This information will store in the Freeze Frame and Failure Records buffers.
- A history DTC stores.

Conditions for Clearing the MIL/DTC
- The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- The MIL/DTCs can be cleared by using the scan tool.

Steps 1 - 4:

Test Description
The numbers below refers to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
2. Program the replacement PCM and perform the crankshaft position system variation learning procedure Refer to the latest Isuzu Technical Communication System (ITCS) information for PCM programming