DoIP: diagnostics over Ethernet and what it means for OBD dongles

DoIP — Diagnostics over Internet Protocol, standardised as ISO 13400 — moves vehicle diagnostics from CAN onto automotive Ethernet. It is already in use across recent premium models and is spreading downwards, so it is worth understanding what it does and does not change for an owner.

Why manufacturers moved

The driver is bandwidth, and specifically software.

Classic CAN runs at 500 kbit/s, and a diagnostic session is further limited by the segmentation described in ISO-TP. Flashing a modern control module means moving hundreds of megabytes. On CAN that is measured in hours.

Automotive Ethernet — 100BASE-T1 over a single twisted pair — runs at 100 Mbit/s, with gigabit variants arriving. The same flash takes minutes.

Secondary reasons matter too: modern driver assistance moves camera and radar data volumes that CAN was never designed for, and IP brings established security and routing tooling with it.

The same pins, different signalling

DoIP reuses the familiar 16-pin connector. Pins 3, 11, 12 and 13 — unassigned in the original OBD-II specification — carry the Ethernet pairs.

That is deliberate: the socket stays compatible, and a car can support both. In practice almost every DoIP vehicle also keeps a CAN gateway for legally mandated emissions diagnostics.

What this means for a standard adapter

The generic OBD-II data still works. Emissions diagnostics remain legally required to be accessible, and manufacturers satisfy that with a CAN gateway on the usual pins. So codes, live data, freeze frame and readiness continue to read normally on a Bluetooth adapter.

Manufacturer-level access does not. Anything beyond the emissions core — module coding, programming, enhanced data, guided routines — moves to Ethernet and needs a DoIP-capable interface, not an ELM327-class dongle.

This is a widening of the gap already described in scan tool limits and UDS Mode 22, not a new kind of restriction.

How a DoIP session works

The flow is recognisably network engineering rather than automotive:

1. Link up. The tester and the vehicle gateway negotiate an Ethernet link.
2. Address assignment. The vehicle typically offers an address, often via DHCP.
3. Vehicle identification. A broadcast request returns VIN and logical addresses of available modules.
4. Routing activation. The tester requests permission to talk to the diagnostic network — this is the step where authentication happens.
5. UDS over TCP. The actual diagnostic services are the same UDS services used on CAN, carried over TCP instead of ISO-TP.

Step 4 is the significant one. Routing activation is a natural security checkpoint, and manufacturers increasingly require a credential there.

The access question

DoIP arrives alongside a broader tightening of diagnostic access. Secure gateways, authenticated sessions and short-lived certificates are becoming normal for anything beyond emissions data.

The stated reason is genuine: a vehicle network reachable by IP is a vehicle network reachable by attackers, and the risks are not hypothetical — see car cybersecurity and CAN injection theft.

The side effect is equally genuine: independent workshops and owners face a higher barrier to work that used to need only a cable. That tension is the subject of right to repair and diagnostic data access.

Which cars have it

Roughly speaking, premium models from around 2018 onwards, spreading into mainstream models from about 2020. It correlates strongly with over-the-air update capability — a car that updates itself overnight has the bandwidth to do so for a reason. See OTA firmware updates and diagnostics.

EV platforms adopted it early, since battery management and inverter software are large and updated often — OBD on electric vehicles.

What to expect in practice

If you own a recent car and a Bluetooth adapter:

• Codes, live data, freeze frame, readiness — work normally.
• Standard PIDs — work normally, subject to what the engine supports.
• Manufacturer data and coding — out of reach, as they largely already were.

If a listing promises full dealer-level access to a 2023 premium model over a cheap Bluetooth dongle, that claim does not survive contact with how the vehicle is built. Related: how to spot a fake ELM327 clone and how to choose an adapter.

The adjacent thing to check

Before worrying about DoIP, check the simpler compatibility question: many 2020-and-newer vehicles use CAN FD on the powertrain bus, and a classic-CAN-only adapter cannot talk to it at all. That trips up far more people than DoIP does — CAN FD explained.

Try it on the free tier of the app — pair an ELM327 adapter and read the supported PID list on your car. Whatever the underlying transport, that list is the honest description of what generic diagnostics will give you.

Read next

• WWH-OBD: the world harmonised standard replacing classic OBD-II