What is trouble code for p o 171??? - 1998 Toyota Corolla

Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1. Try cleaning your MAF sensor (Mass Air Flow) and run a good fuel system cleaner through it.

A/FS or HO2S is contaminated, deteriorated or it has failed Air leaks after the MAF sensor, or in the EGR or PCV system Base engine "mechanical" fault affecting one or more cylinders Exhaust leaks located in front of the A/FS or HO2S location Fuel system supplying too little fuel during cruise or idle (faulty fuel pump or fuel filter) Fuel injector (one or more) dirty or pressure regulator has failed Vehicle driven low on fuel or until it ran out of fuel