I assume the code discussed below is the same as yours. After reading this I wouldn't jump to any O2 sensor conclusions right away.
This was posted earlier by PA 3L SVT:
According to my Service CD, the following list can be causes of code P0171. Once these have been checked, the next test is to see if there is something wrong with the MAF. Might want to start at the MAF first, since cleaning it will be quicker than checking all these. HEGO (or EGO or O2 sensor, all the same thing) isn't even listed here. Don't buy one until you know you need it. If the dealership wants to replace it, ask if they have tested the MAF first. If no, then they are blindly throwing parts at the problem, on your dime. Next thing to ask is why they aren't following the Service Manual troubleshooting instructions. Point them to Diagnostic Routine H41 - DTCs P0172, P0171, P0174, and P0175: Fuel System at the Corrected Fuel Trim. Good luck - this list is long!
quote:
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Possible causes:
Fuel system
-- Excessive fuel pressure.
-- Leaking fuel injector(s).
-- Leaking fuel pressure regulator.
-- Low fuel pressure or running out of fuel.
-- Contaminated fuel injector(s).
-- Vapor management valve (VMV) leaking.
Induction system
-- Air leaks after the MAF.
-- Vacuum leaks (vacuum lines and gaskets).
-- Restricted air inlet.
-- PCV system.
-- Fuel purge system.
-- Improperly seated engine oil dipstick.
EGR System
-- leaking gasket.
-- Stuck open EGR valve.
-- Leaking diaphragm.
Base engine
-- Oil overfill.
-- Cam timing.
-- Cylinder compression.
-- Exhaust leaks before or near the HO2S(s).
l Check intake air system for leaks, obstructions and damage.
l Check air cleaner element, air cleaner housing for blockage.
l Verify integrity of the PCV system.
l Check for vacuum leaks.
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