If not all of the steering wheel control buttons are used for the car PC, you may want some button still work for the car radio.
Because CPJexc is wired between the steering wheel control and the car radio, CPJexc need to bypass the messages which are used for original
equipment(car radio).

If Bypass Steering Wheel Controls to Head Unit is checked, CPJexc bypasses all the messages originate from the steering wheel controls except
the messages used as a button message.
If you want to bypass the button message from steering wheel control to the car radio, check Bypass at the button message list in IBUS Scanner.
Usually the Up Button Message need to bypass to the car radio.
If Bypass Head Unit to Steering Wheel Controls is checked, CPJexc bypasses all the messages originate from the head unit.