Test 1: Confirm car starts, and no IMA codes

The 12V battery should be reconnected at this time.
Start the car. The car will probably start with the IMA motor, but may also start with the 12 V starter.

Since the harness was disconnected from the MCM and BCM, the SOC will probably be at empty, and 4 green regen bars will be lit as the car tries to charge the battery. The charge will continue until the BCM determines that the pack is in fact full, at which point the SOC gauge will do a positive reset and rapidly go to full.

If you see any codes, turn off the car, and do the MCM reset below.

If no codes go to test 2.

if codes are present, read what they are, and contact me so we can determine what is wrong.