Normal Power Down Sequence

The PCM must conduct a normal power down sequence. Whenever the ignition is turned to the OFF or ACC position, modules powered up by the RUN circuit immediately shut down. However the PCM, transaxle control module (TCM), and the battery energy control module (BECM) stay on, until the power down sequence is complete. The PCM keeps the TCM alive by controlling the PCM relay which provides power to the TCM. The BECM is powered directly from the low voltage battery which permits wake-up function when the vehicle is off. During the power down sequence the PCM:

• cuts the power to injectors and ignition coils (engine shut down).
• requests the TCM to disable high voltage inverters.
• disables the DC/DC converter.
• requests the BECM to open the high voltage contractors.
• requests the TCM to discharge the high voltage inverter capacitors.
• opens the PCM relay.

If the power down sequence does not execute correctly, it is considered an abnormal shut down, which may result in the PCM, TCM and BECM storing DTCs.