The four-letter standard that put Ethernet in your OBD2 port — and made a $29.99 cable do what dealer hardware used to.
DoIP — Diagnostics over Internet Protocol, standardised as ISO 13400 — packages vehicle diagnostic messages (UDS) inside Ethernet frames instead of CAN frames. Your car's diagnostic gateway becomes a network device with an IP address; your laptop talks to it the way it talks to any networked machine. That's the entire trick, and it's why a simple, correctly-wired cable can replace four-figure proprietary hardware on modern cars.
Speed. Classic CAN diagnostics run at 500 kbps; modern ECU firmware files exceed 1 GB. At CAN speeds a full flash takes hours and fails often; at DoIP's 100 Mbps the same file moves in minutes. Every flash-heavy platform — BMW F/G, Mercedes 2016+, JLR 2017+, VW/Audi 2017+ — migrated for this reason.
| OBD2 Pin | Function |
|---|---|
| Pin 4 | Chassis ground (CGND) |
| Pin 5 | Signal ground (SGND) |
| Pin 12 | Ethernet TX+ (100BASE-TX) |
| Pin 13 | Ethernet TX− (100BASE-TX) |
| Pin 16 | Battery +12V (powers adapters) |
Rule of thumb: BMW from 2010 (F-Series), Mercedes from ~2016, JLR from 2017, VW/Audi from 2017 — plus virtually every EV launched since 2018. The full model-by-model list lives on the compatibility matrix.