my check engine light came and i went and got the codes pulled and it came out to be "insufficient switching bank 1 sensor 1 lean" or something like that. so i bought a o2 sensor but then when i got home the light had gone out. it had been on for a day or two but now it hasn't come back sense. the car has 87.5k miles on it. should i just return the sensor or go ahead and replace it? if i do replace it, which sensor is that. drive/passenger and before/after cats?

 

id wait a little... sometimes the light will go off for a little while and end up coming right back on

 

Im not positive, but I think bank 1 sensor 1 is the driverside before the cat...Or maybe its passengerside...Time to consult Google....My results are inconclusive.