What are the OBD-II communication protocols?

There are five OBD-II communication protocols: SAE J1850 PWM (used primarily by Ford), SAE J1850 VPW (used primarily by GM), ISO 9141-2 (used by Chrysler and many Asian/European vehicles), ISO 14230-4 (KWP2000, used by many Asian/European vehicles), and ISO 15765-4 (CAN, mandatory on all US vehicles from 2008+). Modern vehicles predominantly use the CAN protocol. When purchasing a scan tool, make sure it supports all five protocols for universal compatibility.