How to play back fake speeds/etc? #39

I've read through the documentation and various issues/questions, and am still at a mental block on how to proceed. I'm only posting this as I've hit a brick wall.

I am hoping to use this to simulate a car ECU, to an attached handheld ODB2 reader, via a USB ELM327 adapter. All I want to play to the ODB2 reader is vehicle speed and engine RPM - no other parameters matter. I want to get to the point where I can input a speed of 10km/hr on my computer, and see 10km/hr displayed on the handheld ODB reader.

The adapter is is available at /dev/tty.usbserial-A78KFBC2, so I am initializing the program with this:
elm -p /dev/tty.usbserial-A78KFBC2 -a 38400 -s car -B 38400 -S /dev/tty.usbserial-A78KFBC2

This seems to respond appropriately with:

2024-02-17 09:12:03,174 - root - INFO - 

ELM327 OBD-II adapter emulator v3.0.0 started on serial communication port "/dev/tty.usbserial-A78KFBC2".

Emulator scenario switched to 'car'
Welcome to the ELM327 OBD-II adapter emulator.
ELM327-emulator is running on serial communication port "/dev/tty.usbserial-A78KFBC2".
Type help or ? to list commands.

At this point, no USB activity lights appear on the EML327 adapter, and the OBD2 device says "communication failure" when trying to connect via ODB2.

Despite trying various commands from the documentation, the only thing I have noticed which results in activity lights on my ELM327 adapter using elm is when I accidentally ran the following - which illuminated the USB activity light, but ultimately didn't establish a connection:

CMD> test car
______Raw command:_______________
2024-02-16 23:28:58,027 - root - INFO - Write forward data: b'CAR\r'
2024-02-16 23:28:58,231 - root - INFO - Read forward data: b'CAR\r?\r\r>'
2024-02-16 23:28:58,231 - root - WARNING - Missing data in dictionary: 'CAR'. Answer:
"b'CAR\\r?\\r\\r>'"
2024-02-16 23:28:58,231 - root - INFO - Unknown ELM command: 'CAR', header=7E0
'<writeln>?</writeln>'

______Command output:____________
'?\r\r>'

At this point I can't tell if I'm barking up the wrong tree and trying to get ELM327-emulator to do something it's not supposed to do, or if I'm missing something obvious. Either way, any advice at all for getting me closer to what I'm trying to do would be greatly appreciated!