The engine is running with too much air and not enough fuel on bank 1. The engine computer is adding extra fuel to compensate, but cannot correct the lean condition enough. Running lean can cause engine overheating and potential damage over time.
Find certified mechanics near you who can diagnose and repair P0171.
For informational purposes only. Diagnostic trouble codes are starting points for diagnosis, not definitive answers. Always consult a certified mechanic for proper diagnosis and repair. Estimated costs vary by vehicle, location, and shop rates.