Care to share your design?
Be happy to share, just need to get around writing it up properly I suppose.
The short of it is just as stooge describes.
You just need:
-generic ebay ELM327 bluetooth OBDII device
-HC-05 bluetooth module (HC-05 because that's able to function as a bluetooth host or whatever it's called)
-whatever display you want, if you want one. I used a .96" OLED display.
I used an ESP32 instead of an Arduino for this because they have a lot more RAM, and I ran out with an Arduino Uno by the time I included a few libraries for the display and for OBDII parsing.
There's a little bit of manual setup for the HC-05 module to pair it to the ELM327 adaptor. Then you write to the HC-05 adaptor from the Arduino/ESP through a serial like most Arduino modules and you're talking directly to the ELM327 module.
There's "ELMDuino" libraries ready to go for the simpler PIDs you'd want to read. For anything from the extended PID set (like oil pressure etc) I had to parse up myself and it's certainly not done particularly well in my code.
I used a Arduino Nano to actually control the valves, and one pin as the open/shut command interface between that and the ESP32. No reason to have separate modules like that except I wanted the functions to be independent.
Thin multicore wire was easy to run from the boot where the valve controller is around under the sill panels and into the centre console where the ESP32 is currently sitting in this prototype stage of the project. Can also power it through the cable from the same boot fuse as the valve controller itself.
Once you've got that data, you can obviously come up with whatever criteria you want for opening and closing the valves.
I found 50% throttle was a sweet spot for never opening under normal commute-type driving, which is what I was after.
Instead of using bluetooth, you can get a USB ELM327 adaptor, crack it open and bypass the USB interface, feeding the ELM327 serial directly into the ESP/Arduino serial pins. I got this working but then decided that I liked the electrical decoupling of the bluetooth approach. I'm sure CANBUS is fairly resilient, and the ELM327 adaptor would also have some isolation but I didn't like the thought of my prototype-maturity project toasting my ECU if something came apart.
