DIAGNOSIS The sensor (auto cook) works by detecting steam humidity. If you're covering the food too tightly with plastic wrap or a lid, or using a container that doesn't allow steam to escape upward, the sensor can't get an accurate read and defaults to a longer time.
FIX 1) Always use a loose cover, like a paper towel, a microwave-safe plate set on top, or a vented plastic lid. Never use airtight seals. 2) Use a reasonably sized, round container that fits comfortably on the turntable. 3) For the best results, use the sensor modes for foods they're designed for (like Sensor Reheat, Sensor Cook for vegetables, etc.) and enter the approximate weight or quantity as accurately as you can when prompted. The sensor works in conjunction with your input.
IF THAT DIDN'T WORK The humidity sensor itself, located behind the interior wall, might be contaminated by grease or dust from past cooking splatters. This requires a professional cleaning or replacement, as accessing it involves partial disassembly. Try running the steam-cleaning method (bowl of water/vinegar) a few times to see if it helps clear any sensor ports.
HEADS UP The sensor works best with moist foods (soups, casseroles, veggies). It's less reliable for dry items like bread or crackers. For those, use time/power settings instead.