This code does not mean the oxygen sensor is at fault. More than likelyyou have a vacuum leak. I have seen numerous intake manifold gaskets leak at the gasket sealing the air in the runers. Take some 2+2 Gummcutter from the auto parts store and start your engine. Spray the gummcutter down around the intake manifold gasket and see if the engine revs or satlls. If it does you found your leak. there are other possibilities like plugged fuel filter and a bad MAF (Mass Air Flow) sensor. Here is a TSB from Ford about the lean code.
MALFUNCTION INDICATOR LAMP (MIL)ILLUMINATED - SYSTEM LEAN DIAGNOSTICTROUBLE CODES (DTC'S) - SERVICE TIPS
FORD:2000 Contour2000-2002 Escort2000-2003 Escort ZX22000-2004 Crown Victoria, Focus, Mustang, Taurus2002-2004 Thunderbird2000-2003 Windstar2000-2004 Econoline, Excursion, Expedition, Explorer, F-Super Duty, Ranger2001-2004 Escape2004 Freestar2000-2004 F-Series
LINCOLN:2000-2002 Continental2000-2004 LS, Town Car, Navigator2002-2003 Blackwood2003-2004 Aviator
MERCURY:2000 Mystique2000-2002 Cougar2000-2004 Grand Marquis, Sable, Mountaineer2004 Monterey
This article is intended to aid in diagnosing DTC's P0171, P0174, P1130, P1131, P1150, P1151, P2195, or P2197 (system lean or lack of HEGO switches) when a vacuum leak is present. HEGO sensors, MAF sensors, and PCM replacements are not an effective repair when a vacuum leak is causing the above DTC's.
Perform the following inspections/repairs when the above codes are found in memory. Procedure provides instructions on how to make comparisons of the total fuel corrections (using scan tool or equivalent) at idle and high RPM's to help determine if a vacuum leak is the root cause of the DTC's.
NOTE FREEZE FRAME AND ADAPTIVE FUEL VALUES (ASSOCIATED WITH "LONGFT" PID) WILL NOT BE AVAILABLE IF A KAM OR OBDII RESET WAS RECENTLY PERFORMED.
NOTE FREEZE FRAME DATA WILL INDICATE THE ENGINE AND AMBIENT CONDITIONS WHEN THE DTC WAS SET. THESE ARE IMPORTANT BECAUSE THE VACUUM LEAKS MAY OCCUR ONLY WITHIN SPECIFIC TEMPERATURE RANGES AND MUST BE DUPLICATED TO DETECT THE LEAK.
NOTE FUEL TRIMS AT IDLE ARE PARTICULARLY SENSITIVE TO VACUUM LEAKS SINCE THE UN-METERED AIR "LEAKAGE FLOW" IS A HIGHER PERCENTAGE OF TOTAL AIRFLOW AT IDLE THAN AT PART THROTTLE. THE BAROMETRIC PRESSURE (BP) PID IS NOT RECOMMENDED TO VIEW WHEN DIAGNOSING A VACUUM LEAK. BP IS AN INFERRED PID CALCULATED DURING HIGHER ENGINE LOADS.
A TYPICAL VACUUM LEAK WHICH MAY SET A LEAN CODE DTC WILL HAVE TOTAL CORRECTION OF AROUND +20% OR GREATER AT OR NEAR IDLE (DEPENDS ON CALIBRATION)