I'm currently at a loss. We bought a 2015.5 with 86K. Everything looks great and we were (and still are) happy about it, but after about 120 miles after purchase the check engine light came on. The code was P2096 Post Catalyst Fuel Trim System Too Lean Bank 1. I called the dealership (not a Volvo unfortunately). They came back and said that an O2 sensor needed replaced (no surprise) and the thermostat as well (that code was not showing before, but it's their dime). They replaced them the next week. All was good and the exhaust smelled fine. Then again at about 120 miles the check engine light came on again with the same code! I checked, and there is indeed a new sensor. It's the one on the right side as you are looking toward the front of the car.