HI,
I had P0171 and P0174 fault codes system lean bank 1 and system lean bank 2 on a VF SV6 advised to run 98 for 2 full tanks as petrol may have been the cause and if engine fault light still on replace oxygen sensors, filled up tank with 98 drove it for a day engine fault light still on. Next day fault light still on so I checked the fuses they looked OK just brown on contacts but I replaced three ( engine control module, ECM V6 INJ / IGN, engine control module IGN ) started engine, No fault light don't know which one fixed it but you might won't to replace yours.