What does the OBD II function test assess?

The function of the OBD II (On-Board Diagnostics II) system is multi-faceted, and this is why the correct answer encompasses all the options provided.

The OBD II function test is essential in assessing various aspects of the vehicle's emissions control system. Firstly, it checks the ability of the OBD II system to communicate with diagnostic tools. This communication is crucial for identifying issues, as it allows mechanics and inspectors to interact with the vehicle's onboard computer to retrieve information about the system's status.

Secondly, the OBD II function test determines the readiness of system monitors. These monitors perform self-checks on different components of the emissions system. For a vehicle to pass emissions testing, certain monitors must show as "ready," indicating they have been completed successfully after a specified drive cycle.

Lastly, reading Diagnostic Trouble Codes (DTCs) is a vital component of the OBD II function test. DTCs provide information about specific malfunctions within the vehicle's systems, particularly related to emissions. Inspectors utilize these codes to diagnose problems and ensure compliance with emissions standards.

Since the OBD II function test encompasses communication, system monitor readiness, and the reading of DTCs, selecting all three areas as part of its assessment underscores