Start sequence with OEM controllers - communication logic

I'm wondering how OEM VCUs communicate with their motor controllers and switch electronics during start-up of an EV.

Besides the electrical start-up procedure with contactors and pre-charging, VCUs send a bunch of signals to the controller during the starting sequence (via CAN bus). Some of these signals are OEM-specific, but usually they follow a common logic. I figured out some signals that might be relevant:

• Key position (off/acc/on/crank)
• Motor mode (standby/torque/regen)
• Gear lever position
• BMS message about precharge activity

The question is how these messages interact with electrical operations and in which order. These are common hardware controls:

• KL15 +12V starts the controller and CAN bus communication
• HV interlock
• Main contactor
• Precharge circuit (if not included in the controller)

The goal is an open VCU for OEM parts control. I have an example OEM CAN matrix, but don't have any expertise in this field.

I would greatly appreciate any hint with OEM insights. I know that this knowledge is proprietary, but it might improve my/our understanding of OEM parts and increase the number of usable parts from salvage vehicles.