OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J/1979 defines many PIDs, but manufacturers also define many more PIDs specific to their vehicles. All light duty vehicles (i.e. less than 8,500 pounds) sold in North America since 1996, as well as medium duty vehicles (i.e. 8,500-14,000 pounds) beginning in 2005, and heavy duty vehicles (i.e. greater than 14,000 pounds) beginning in 2010, are required to support OBD-II diagnostics, using a standardized data link connector, and a subset of the SAE J/1979 defined PIDs (or SAE J/1939 as applicable for medium/heavy duty vehicles), primarily for state mandated emissions inspections.
Typically, an automotive technician will use PIDs with a scan tool connected to the vehicle’s OBD-II connector.
- The technician enters the PID
- The scan tool sends it to the vehicle’s bus (CAN, VPW, PWM, ISO, KWP. After 2008, CAN only)
- A device on the bus recognizes the PID as one it is responsible for, and reports the value for that PID to the bus
- The scan tool reads the response, and displays it to the technician