ISO 13400-4:2016 specifies a minimum set of diagnostic Ethernet connector requirements which are based on ISO 15031‑3. The ISO 15031‑3 diagnostic connector is referenced by legislation in many countries.

The diagnostic connection specified in this part of ISO 13400 consists of two mating connectors: the vehicle connector and the external test equipment connector as specified in ISO 15031‑3.

ISO 13400-4:2016 specifies:

- the functional requirements for the vehicle connector. These functional requirements are separated into two principal areas: connector contact allocation and electrical requirements for connector and related electrical circuits;

- the functional requirements for the external test equipment connector. These functional requirements are separated into two principal areas: connector contact allocation and electrical requirements for connector and related electrical circuits.

Two (2) different connector layouts and pin-outs are specified in this part of ISO 13400:

a) Ethernet pin assignment option 1 (see Annex A);

b) Ethernet pin assignment option 2 (see Annex B).

Historically, option 1 is specified to meet Ethernet pin assignment of road vehicles already launched onto the market and may be used to resolve conflicts with vehicle manufacturer-specific usage of discretionary pins, e.g. pins 1 and 9.

Option 2 is specified to meet the Ethernet pin assignment of road vehicles to resolve conflicts with vehicle manufacturer-specific usage of discretionary pins, e.g. pins 3 and 11.

A discovery/identification and activation method of the vehicle's Ethernet via the "Ethernet Activation Line" is specified in ISO 13400‑3.