What should you do after turning off the engine and turning the key back on?

After turning off the engine and turning the key back on, releasing the park brakes and waiting for air pressure to stabilize is the appropriate action to take. This step is crucial as it ensures that the vehicle's air brake system builds sufficient air pressure to operate effectively.

When the key is turned back on without starting the engine, the air compressor has not yet started running, which means that the vehicle has no air supply for the braking system. By releasing the park brakes, you can assess whether the air system is appropriately functioning and if it can maintain pressure. This step is part of the overall safety check and pre-trip inspection process, ensuring that all systems are operational before proceeding with driving.

Checking for leaks, starting the engine to build air pressure immediately, or testing the service brakes immediately would not be suitable immediate actions right after shutting off the engine, as these choices may overlook the necessary assessment of air brake functionality and initial stabilization needs.