The openxc-dashboard tool available as a part of the OpenXC Python library can be used to view the output of the vehicle interface over USB or UART. This is the most useful tool when determining which vehicle signals are working.

The Python library can be installed with pip:

$ pip install openxc

Once installed, you can use any of the tools it provides.

# Show a dashboard summary of the current values
$ openxc-dashboard
...

# Show a real-time stream of all messages
$ openxc-dump
...

# Send an OBD-II diagnostic request
$ openxc-diag --message-id 0x7df --mode 0x3
...

It may also be necessary to check the current version of the software you have on a vehicle interface - the openxc-control tool can tell you that.

$ openxc-control version
Device is running version 1.1

You can also write a message back to the vehicle interface (which may or may not write it through to the CAN bus, depending on if it is an approved signal or not):

$ openxc-control write --name steering_wheel_angle --value 42.0

You can write raw CAN messages, too:

$ openxc-control write --bus 1 --id 42 --data 0x1234