Re: so how often do you replace Oxygen Sensor?
The $99 code readers will do what they say, read the codes, it's up to you to determine what's really wrong. Example, a 2001 Sante Fe, my Actron CP-9145 code reader says P0171 "system too lean, bank 1". Duh, that leaves a lot of possibilities, so what could it be? Dealer inspection turned up a defective timing belt self adjuster and the belt jumped timing, Hyundai's 100k/10 year warranty fixed that and the mass Air Flow Sensor ($$$) was also replaced, code went away. Good luck with OBDll, the old Ford EEC-IV system codes at least pointed you to the problem area but still required common troubleshooting sense.