Ok, I will give it a try:
It means the fluid level in the respective system is low (probably a leak). Low system pressure would be indicated by a 'HYD_ PRES LO' alert.
The HYD_ QTY LO alert is normally only displayed if the HYD SYS is in manual mode.
Here is an excerpt from the OM-B
- If System 1,2,3 is affected: Fluid in the respective hydraulic system is less than 2.5 gallons (manual mode only)
Note: This alert is displayed when 10 quarts of fluid remain in the hydraulic tank. Alert will not normally be displayed during automatic mode. When automatic mode senses fluid is at 10 quarts, it will deactivate all pumps in the system and display 'HYD 1, 2, 3 OFF' alert. Therefore 'HYD 1, 2, 3 QTY LO' alert will be displayed only during manual mode or when automatic mode cannot compensate for low quantity condition.
Hope this helps,
DBate