If hydraulic system pressure is normal while the pump is running but ceases after the engine is shut off, what does this suggest?

When the hydraulic system pressure is normal while the pump is running but falls to zero after the engine is shut off, this typically suggests that there is no air pressure in the accumulator. The accumulator is a crucial component in hydraulic systems as it stores energy in the form of hydraulic fluid under pressure. It also helps to maintain pressure in the system and can dampen fluctuations in pressure during operation.

When the pump is operating, it maintains the system pressure by continuously supplying hydraulic fluid. Once the engine is turned off, if the pressure immediately drops to zero, it signifies that the accumulator is not holding any pressure, likely because it is either empty or has failed. This condition prevents the accumulator from performing its function of maintaining pressure, resulting in a sudden drop once the pump (and therefore pressure) is removed.

This understanding leads to the conclusion that the absence of air pressure in the accumulator is directly related to the loss of hydraulic pressure observed when the engine stops, thus confirming the correctness of the selected answer.