Jun 2, 2015 · 6.4 Hemi. P0171 is a lean mixture code for bank one (pre cat, at the air/fuel sensor) and P2097 is a rich mixture codes for bank one (post cat, at the O2 sensor). Basically, the engine detects it is getting too much air, so it adds fuel and the post cat sensor detects the added fuel and throws a rich mixutre code.