CAN FD
Workshop glossary › Diagnostics & protocols · UpdatedCAN with Flexible Data-rate. Same physical wiring as classic CAN but with payloads up to 64 bytes and bit rates up to 5 Mbit/s. Shipping on most cars built from around 2020.
CAN FD (CAN with Flexible Data-rate) is Bosch's 2012 successor to classic CAN. It uses the same wiring, same connectors, and the same arbitration rules, but during the data phase it switches to a higher bit rate (up to 5 Mbit/s) and allows payloads up to 64 bytes instead of 8.
Why workshops care: a lot of modern ECU programming — security access, large flash blocks, sensor calibration tables — moves data fast enough that classic CAN became a bottleneck. Vehicles built from around 2018 onward (Mercedes from 2019, BMW G-series, modern PSA/Stellantis platforms) increasingly run CAN FD on at least one network segment.
A classic-CAN scan tool can still read OBD-II generic data on a CAN FD car, because the diagnostic gateway falls back to classic CAN for the OBD-II protocol. But brand-specific diagnostics, ECU coding, and module replacement need a CAN-FD-capable tool.