Using my primitive prison tools, I believe the arrangement for the driver's side was o2 socket, 4" extension, swivel, and 12" extension w/ breaker bar. With my tools/patience I could not find a way to loosen from below. I slid the o2 socket (not crow foot) on sensor from underneath and loosened from above. I didn't remove surrounding components, which added to the fun. Disclaimer - Use this method after trying other more logical options.