ISO 15765-4
Workshop glossary › Diagnostics & protocols · UpdatedThe standard that adapts CAN bus for OBD-II / EOBD diagnostics. Mandatory on US OBD-II vehicles from model year 2008.
ISO 15765-4 defines how OBD-II diagnostic services run over a CAN bus. It pins down the bit rate (250 kbit/s or 500 kbit/s), the CAN IDs used for diagnostic requests (0x7DF broadcast, 0x7E0–0x7E7 for specific ECUs) and the transport layer that segments longer messages into multiple CAN frames.
From OBD-II model year 2008, ISO 15765-4 is the only permitted diagnostic protocol on the US market. EOBD followed shortly after. Any modern generic scan tool defaults to ISO 15765-4 and will only fall back to older protocols (J1850, ISO 9141-2, KWP2000) when explicitly asked to.