Which of the following is an example of an OBD II non-continuous monitor?

The oxygen sensor is an example of an OBD II non-continuous monitor because its functionality is tested only under specific driving conditions and not continuously throughout every drive cycle. OBD II systems use a variety of monitors to evaluate the performance of different vehicle components, and non-continuous monitors require certain criteria or conditions to be met before they are tested.

In the case of the oxygen sensor, the testing is dependent on factors such as engine load, temperature, and other operational states that don’t occur continuously while driving. This can be distinct from continuous monitors that check their respective components more frequently or are active during most driving conditions.

The other options listed are components that might have different testing paradigms, but they are not classified as non-continuous monitors in the same way that the oxygen sensor is. For instance, transmission fluid level and battery voltage are monitored continuously while the vehicle is in operation, ensuring that any irregularities can be addressed promptly. Radiator temperature can also be monitored consistently, providing ongoing feedback about the vehicle's cooling system. Thus, the oxygen sensor stands out for its specific testing requirements, which align with the criteria for non-continuous monitoring.