What will cause the FAULT light to illuminate on the IDG DISC switchlight?

• A. High CSS oil temperature or Low oil pressure
• B. Low CSS oil temperature or High oil pressure
• C. High oil temperature and high engine torque
• D. Low temperature and low oil pressure

Answer: (A)

The IDG DISC switchlight fault indicator is tied to the lubrication and cooling condition of the Constant Speed Shaft drive. It will illuminate if the CSS oil temperature is too high or if the CSS oil pressure is too low. A high oil temperature means the oil isn’t removing heat effectively from the drive, risking overheating; a low oil pressure means there isn’t enough lubrication to protect gears and bearings. In either case, the fault light signals a condition that could damage the IDG, prompting protection actions. The other scenarios—low oil temperature or high oil pressure, or a combination like low temperature with low pressure—do not indicate a fault in this monitoring logic, so they won’t trigger the FAULT illumination.