In this video I explain the CAN-BUS diagnosis step by step. I have a car for this video that has a major CAN-BUS problem, so my scan tool cannot communicate with multiple control units (Engine, Transmission, ABS, A/C, ..), so I explain how to start the diagnosis on the CAN-BUS from the more accessible points to find the problem. I explain how to test the CAN-BUS resistance, how to test the CAN-BUS voltage, how to test it for the short to ground, then how to narrow it down to isolate the problem area for finding it easier. I also explain the CAN-BUS wiring diagram.