When my 130 lb wife rides in the passenger seat of our 2018 Forester Premium, she needs a personal seat cushion. Using the cushion, the sensor does not read her electrical conductivity, and turns off the airbag. She doesn't want to ride without an airbag, so she must always drive when we are together (unless she rides in the back!) The technician at Lancaster Subaru checked with the Company and told us there was no fix for this, and we were prepared to purchase a new 2019 model with softer seats, although we have only 3500 miles on this vehicle.
My son-in-law consulted a local forum which claimed that the newer vehicles use electrical conductivity to determine if a sizable adult is sitting in the passenger seat, rather than weight. He suggested using a 12" x 15" piece of aluminum foil inside the personal seat cushion (unzipped and placed in the bottom of the cushion, next to the seat) to provide capacitance to the sensor. Interestingly, this solution works perfectly for us, and I can drive again, without buying a new Subaru! Since it is entirely passive, it should not affect the operation of the switch or defeat the intent of the airbag-off for children in the front seat. The cushion is reserved ONLY for my wife, who even takes it into restaurants and hard-chair establishments. No problem there except for a faint crinkling upon sitting down. has anyone else tried this?