malfunction; defective operation; operational failure
Technical term for when a machine, device, or system does not work as intended. Common in engineering, IT, and product documentation.
This device is malfunctioning.
We are investigating the cause of the operational failure.
故障 is a more general and common word for breakdown or failure, while 動作不良 is a technical term specifically referring to improper operation or malfunction.
Compound of 動作 (operation, movement) and 不良 (bad, defective). A straightforward technical term.