What indicates that the electric motor is functioning properly in a hydraulic system?

The correct answer highlights that a properly functioning electric motor in a hydraulic system operates while the engine is running. This indicates that the motor is receiving the necessary power supply and is capable of driving the hydraulic pump to create the required pressure for system operation. The motor's activation under these conditions is critical, as it demonstrates that the electric motor can effectively contribute to the hydraulic system's functionality while the engine is providing power.

In contrast, the options that mention no sounds or failure to operate when the engine is not running do not provide a clear indication of proper function. An electric motor may still be functioning even if it emits sounds, which can be normal depending on the design and load conditions. Furthermore, if the motor does not operate when the engine is off, it may simply mean that it depends on the engine's power source, but does not necessarily imply a malfunction. Finally, the option regarding activation when the brakes are applied relates to a specific scenario rather than a general indicator of electric motor functionality, making it less relevant in determining overall operational status. Thus, the ability of the motor to operate while the engine runs is a clear and essential indicator of its proper functioning within the system.