What process involves checking the fluid level by removing a fill plug?

The correct process referred to in this question is the differential fluid check. This procedure entails removing a fill plug to assess the fluid level within the differential. This step is crucial in maintaining proper lubrication of the gears within the differential, which is essential for ensuring optimal performance and longevity of the vehicle's drivetrain.

During this check, if the fluid is at the appropriate level, it should be just below the fill plug. Observing this offers insight into whether the differential is properly maintained; low fluid levels can result in increased friction, overheating, and potential damage to the components inside the differential.

In contrast, engine oil, transmission fluid, and power steering fluid checks typically involve other methods, such as using a dipstick or reservoir markings, rather than removing a fill plug to assess fluid levels. Thus, the differential fluid check specifically utilizes this method, helping ensure the differential operates efficiently.