What should be done before removing the fill plug on the planetary final drive fluid service?

Before removing the fill plug on the planetary final drive fluid service, positioning each wheel parallel to the ground is crucial for obtaining an accurate fluid level. When the wheels are level, it ensures that the final drive housing is also level, which allows for a proper reading of the fluid level during the service. This step is essential for maintaining the correct amount of fluid in the system, as having the vehicle in an unlevel position can lead to an inaccurate assessment, potentially resulting in overfilling or underfilling.

Other options, such as ensuring all wheels are locked or draining the fluid completely, do not specifically address the accurate measurement of fluid levels necessary for proper service. Warming up the engine, while important for overall engine performance and fluid viscosity, does not directly relate to the accurate determination of fluid levels in the planetary final drive system. Thus, having the wheels parallel to the ground is the most effective way to ensure proper servicing of the final drive fluid.