Diagnosis
The laser particle sensor window is likely obstructed. Dust or fibers can accumulate on the small, recessed sensor lens inside the front intake, blinding it.
How to Fix It
Power off the unit. Use a can of compressed air, holding it upright, to blast short bursts directly into the sensor port (a small rectangular opening inside the front intake area). A cotton swab lightly dampened with isopropyl alcohol can gently clean the exterior lens surface.
If That Didn't Work
The sensor may be in a calibration cycle. Leave the unit powered on in Auto mode in a clean environment for 24 hours. The sensor logic requires a baseline of 'clean' air to compare against.
Heads Up
The Auto mode reacts to particulate matter (PM2.5/PM10), not VOCs or odors. Air freshener, cooking smoke, or candles may not trigger a response unless they produce visible aerosol particles.