I have a 2011 Forester 2.5 non-turbo with approximately 100k miles. I've been trying to diagnose a P0171 code (Lean code) and am coming up with nothing. I work in the automotive field and smoke tested the emission system to see if I had a vacuum leak and came up with nothing. I have a CRP123 launch scan tool with which I can see live and freeze frame data and am just wondering the next step to take for the diagnostic process. For some reason, I am leaning towards the bank 1 sensor 1 A/F sensor as the vehicle is approaching 100k miles and I've been experiencing a gradual decrease in MPG. Could anyone please chime in if they had a similar experience or have any words of advice on how to proceed? It would be greatly appreciated. Thank you in advance!