What specific parameters are checked during an OBD test?

During an On-Board Diagnostics (OBD) test, the focus is primarily on evaluating the vehicle's emissions control system. This involves checking trouble codes and readiness monitors. Trouble codes provide information about any detected malfunctions within the vehicle's systems, especially those related to emissions controls. These codes help identify specific issues affecting the vehicle's performance or emissions output.

Readiness monitors, on the other hand, are part of the OBD system that ensures various emissions-related components are functioning correctly and have completed necessary self-checks since the last time the vehicle was reset or had its battery disconnected. These monitors help determine whether the vehicle is ready for emissions testing by confirming that the vehicle's emission systems are operational and that certain conditions have been met, indicating that the vehicle can pass an emissions test.

In contrast, checking engine oil levels and battery age, assessing fuel efficiency and tire pressure, or measuring vehicle weight and dimensions do not provide relevant information regarding the emissions control system and are not part of the OBD test parameters.