The diagnostic tool cannot be connected to the car computer, what should I do?

Why are there two sets of communication lines? One group of high-speed CAN, the other group of low-speed CAN. High-speed CAN is for the power system, and low-speed CAN is for the comfort system. Volkswagen is called Power CAN and Comfort CAN respectively.

There is voltage, but it does not prove that the CAN communication line is good. Next we use the oscilloscope to look at his waveform.