OBD-II PIDs - CAN (11-bit) Bus Format

CAN (11-bit) Bus Format

The PID query and response occurs on the vehicle's CAN Bus. Standard OBD requests and responses use functional addresses. The diagnostic reader initiates a query using CAN ID $7DF, which acts as a broadcast address, and accepts responses from any ID in the range $7E8 to $7EF. ECUs that can respond to OBD queries listen both to the functional broadcast ID of $7DF and one assigned ID in the range $7E0 to $7E7. Their response has an ID of their assigned ID plus 8 e.g. $7E8 through $7EF.

This approach allows up to eight ECUs, each independently responding to OBD queries. The diagnostic reader can use the ID in the ECU response frame to continue communication with a specific ECU. In particular, multi-frame communication requires a response to the specific ECU ID rather than to ID $7DF.

CAN bus may also be used for communication beyond the standard OBD messages. Physical addressing uses particular CAN IDs for specific modules (e.g., 720 for the instrument cluster in Fords) with proprietary frame payloads.