What should you do before performing maintenance on a vehicle supported by a jack?

Before performing maintenance on a vehicle supported by a jack, it is crucial to check the stability and security of the vehicle. This step ensures that the vehicle is properly supported and reduces the risk of it slipping or falling during the maintenance work, which could lead to serious injuries or accidents.

By confirming that the jack is correctly positioned and that the vehicle is stable, you are prioritizing safety. This involves verifying that the jack is not on an uneven surface, that the jack stands are properly placed if used, and that the vehicle is secured against accidental movement.

The other options, while they may pertain to general vehicle handling, do not directly address the critical safety concerns associated with working under a jacked vehicle. Revving the engine could create unnecessary vibrations, potentially compromising the vehicle's stability. Removing tools from the area is a good practice but secondary to ensuring the vehicle's security. Similarly, making sure the vehicle is unlocked can be important for access but carries much less immediate risk compared to the stability of the jack support during maintenance.