Normal Power Down Sequence

The TCM must conduct a normal power down sequence. Whenever the ignition is turned to the OFF or ACC position, modules powered up by the ISP-R circuit immediately shut down. However the PCM, TCM, and the battery energy control module (BECM) stay on, until the power down sequence is complete. The PCM and TCM stay powered by controlling their own dedicated power relays. 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 TCM:

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

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