A generator includes a main cavity and a shaft located in the main cavity. The shaft is configured to be connected to an auxiliary power unit (APU) and rotated by the APU. The generator is configured to generate power based on the rotation of the shaft. A fluid system is configured to receive a fluid from the APU, flow the fluid through the main cavity and return the fluid to the APU through a fluid scavenge channel. A filter is configured to filter the fluid from the main cavity to the fluid scavenge channel and a sensor is configured to detect a characteristic of the fluid at the filter.