This part of ISO 14229 specifies data link independent requirements of diagnostic services, which allow a diagnostic tester (client) to control diagnostic functions in an on-vehicle Electronic Control Unit (server) such as an electronic fuel injection, automatic gear box, anti-lock braking system, etc. connected on a serial data link embedded in a road vehicle. It specifies generic services which allow the diagnostic tester (client) to stop or to resume non-diagnostic message transmission on the data link. This part of ISO 14229 does not apply to non-diagnostic message transmission or to use of the communication data link between two Electronic Control Units. It does not specify any implementation requirements.