CAN FD
Diagnostics & Protocols · 6 specs
Direct Answer
CAN FD (Controller Area Network with Flexible Data-Rate, developed by Bosch in 2012 and standardized under ISO 11898-1:2015) extends classical CAN bus to overcome bandwidth bottlenecks in modern vehicles. Increasing payload size from 8 bytes to 64 bytes and accelerating data transmission during the data phase from 500 kbps up to 2, 5, or 8 Mbps.
Source: ISO 11898-1:2015 (Road vehicles — Controller area network — Part 1: Data link layer and physical signalling) / Bosch CAN FD Specification · Last reviewed Aug 28, 2026
Specs
| Standardization | ISO 11898-1:2015 (Standardized CAN FD) |
| Data Payload Capacity | Expanded from 8 bytes (Classic CAN) up to 64 bytes per frame (eightfold increase) |
| Dual Bit-Rate Architecture | Arbitration Phase: 500 kbps (preserves long wire distance and arbitration) | Data Phase: Switched to 2 Mbps, 5 Mbps, or 8 Mbps |
| Bit Rate Switch (BRS) Bit | Single control bit in header switches transceiver clock into high-speed mode and back after CRC |
| CRC Integrity Protection | 17-bit CRC for payloads up to 16 bytes; 21-bit CRC for payloads up to 64 bytes (with 4-bit stuff-count field) |
| Modern Vehicle Deployments | Mandatory in modern ADAS radar/camera fusion, encrypted gateway security, and EV battery management systems (BMS) |
Dual Clock Rate Mechanics
Traditional CAN bus speed was physically limited by signal propagation delay across the vehicle during arbitration. CAN FD solves this by running two clock speeds in one frame: it starts at 500 kbps so all ECUs can safely arbitrate priority, flips the BRS bit, transmits the massive 64-byte payload at 5 Mbps, and drops back to 500 kbps for the ACK bit and end-of-frame.