Originally posted by james05:
I also checked haynes manual says oxygen sensor.



Haynes....BAH! Better than nothing, I suppose....if you're out of Charmin...


Here is the list of possible causes for DTC P0171, P0172, P0174, and P0175 from the Service CD. Maybe it's just me, but I don't see any mention of an O2 sensor fault as a possible cause.

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H41 DTCs P0172, P0171, P0174 AND P0175: FUEL SYSTEM AT THE CORRECTED FUEL TRIM

Diagnostic Trouble Codes (DTCs) P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit.

DTC P0172 bank 1 and DTC P0175 bank 2 indicate the fuel/air ratio is too rich. The fuel trim system is at the lean correction limit.

DTCs HO2S Reference list:

-- HO2S-11 = DTCs P0171 and P0172

-- HO2S-21 = DTCs P0174 and P0175

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.

l Are any of the above concerns present?

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Steve


98 Contour SE Sport 2.5 Duratec ATX The wifey's car 89 Taurus SHO - 246K miles 94 SHO ATX - 190K 1997 F-150 5.4L ATX - The Workhorse 150K. ANY THREAD WITH "OMG" or "WTF" ETC IN THE TITLE WILL BE IGNORED!