Edie ... 4/2/2010
1999 Mazda Protege ES 4 Cyl 1.8L
P0171 code bank 1 is it possible that the o2 sensor is bad?
p0171 is a lean code meaning that the o2 sensor registered too much air and not enough fuel. the possibility of it being an oxygen sensor is slim however because the ecm willl set a no or limited activity code for that sensor. most likely possibilities are vacuum leak at engine. low fuel pressure, or misbehaving mass air flow sensor. there are a few rare occasions were these problems are caused by improper engine calibrations( meaning that the ecm does not have a wide enough range for these occurance- requiring reprogramming the computer at the dealer) try thje vacuum leak first though and good luck