On GM cars/trucks, the high speed bus goes to sleep and fully shuts down ~10 seconds after the key is turned OFF.
the SWCAN bus stays awake for at least 5 minutes or more after the last door is closed and vehicle locked. If retained accessory power is active, expect the SWCAN bus to be awake (albeit not that much traffic) for 10-15 minutes before fully sleeping.
The high speed bus can NOT be woken up via bus activity. All of the modules on the high speed bus are only woken up (and put to deep sleep) via a discrete “serial data enable” +12v power circuit from the BCM.
SWCAN modules obviously all support HVWU (high voltage wakeup, via a +12v pulse and then a wake up message broadcast on ID $100. Usually its the RCDLR (remote control door lock receiver) that wakes the truck up (via HVWU on SWCAN) because you hit unlock on the remote keyless entry. But if the truck is already unlocked, but in deep-sleep, the DDM, PDM (drivers door module and passenger door module), and BCM can also force HVWU if a door is opened while the truck is asleep.
Some low priority SWCAN messages are event-triggered, but most messages are broadcast on set periodic intervals.
PMM (power mode master, ie ignition switch status) messages are broadcast by the BCM on 5 second intervals, but they are also event-trigger based (if an immediate PMM change is detected, like turning the key off)
The BCM is the gateway between high speed CAN and SWCAN. Any messages that have to get between the two busses get passed/translated via the BCM.
The BCM, VCIM (onstar module) are the only modules that are on both highspeed CAN and SWCAN. On the newest Global-A vehicles, the HMI (human machine interface) module is on both SWCAN and high speed CAN as well…
But yeah, the BCM is the gateway.
pre-global-A CAN-based GM vehicles (like mid 2000’s-ish to early 2010’s-ish) only used LIN two places…for the BCM to communicate with the compass module…and on vehicles with front auto/one-touch-up windows, the PDM and DDM communicated with the window motors themselves via LIN. But otherwise, everything else interior is SWCAN.
Global-A saw much more widespread use of LIN, for HVAC controls/radio head units, all windows, etc.
I dont know much about other makes/models of cars/trucks, but Im happy to answer most GM questions…