P1621

Diagnostic Chart:

Since this diagnostic pertains to an internal vehicle control module (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 control module stores the DTC in history after the first failure but will not illuminate the Malfunction Indicator Lamp (MIL).
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/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 numbers below refer to the step numbers on the diagnostic table.
2. This test checks if communication can be established between the scan tool and the VTD.
3. This test checks for any opens in the serial data circuit between the VCM and the VTD. This also checks for any intermittent malfunctions associated with the serial data circuit.
4. This step is to determine if the condition that set the DTC is still present. The engine must be cranked in order to set this DTC. If the condition is present, the engine will start and then stall, indicating the VCM is disabling fuel.
7. Use a scan tool in order to clear and check for any DTCs in all the modules connected to the Class 2 Serial Data circuit (VCM, VTD, ATC, and BCM).