Unfortunately, my OBDII port is filtered in that it'll only spit out CAN messages with an associated PID request.
I was able to find two different buttons' long-press changes, and they're both buttons I could use for this, either one button as a mode switcher, or both buttons as a toggle, or either and both, which I prefer, explained below.
I'll need to do some reading to figure out how to code different states of the exhaust valve control (no override, override open, override closed) and I think I'll want to build it as follows:
default: no override
longpressButtonA: override open (loud mode)
longpressButtonB: override closed (quiet mode)
longpressBothButtons: stop override (stock operation)
Should anyone have any insights to share about how to achieve this, or other projects I could look at for inspiration (cough, lazyweb), that'd be great.
I've started to look at other Particle guides but they seem as yet only distantly helpful. (Reminder: I'm not a programmer, so please be kind.)