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.