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i'm getting p0171 and p0174.system too lean bank 1 and 2.i was going to replace the forward 2 first and see if that will fix it.
 

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Read the descriptions below. This has nothing to do with your rear o2 sensors. Both Bank 1 (Pass side) and Bank 2 (Drivers side) front O2 sensors are seeing a lean condition. Since you are getting codes from both sides, I doubt the O2 sensors are bad. Read through the below diagnostic subroutine, and most likely you will find your issue.

Since it has nothing to do with your two rear o2 sensors, MIL Eliminators will do you no good.



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

Diagnostic Trouble Codes (DTCs) P0171 bank (1) (cylinder #1) and DTC P0174 bank (2) indicate the fuel/air ratio is too lean. The fuel adaptive 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 adaptive syste 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.

-- Contaminated injector(s)

Induction system

-- Air leaks after the MAF.

-- Vacuum leaks.

-- Restricted air inlet.

-- PCV system.

-- Fuel purge system.

-- Improperly seated dip stick.

EGR

-- 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 air intake for leaks, obstructions and damage.

l Check air filter, air filter housing for blockage.

l Verify integrity of the PCV system.

l Check for vacuum leaks.
 
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