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1999 Ford Expedition Question: HAVE A P1151 CODE... WHAT COULD THIS BE? IS IT VACCUME, MAF??



CHADAUTO77, 5.4L V8, Rocky Mount, NC, December 19, 2011, 11:12


2 Answers
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  • Answer #1

    December 19, 2011, 11:55

    It is an oxygen sensor code.
    P1151 OBD Trouble Code
    NOTICE: The information contained on this site is presented for information only. OBD-Codes.com is not responsible for any actions you take on any vehicles. If you have any doubt as to repairs on your vehicle, please contact a qualified technician.

    Technical Description
    Lack of HO2S-21 Switch, Sensor Indicates Lean

    What does that mean?
    A Heated Exhaust Oxygen (HO2S) sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

    You will likely not notice any drivability problems.

    A code P1151 may mean that one or more of the following has happened:

    Short to VPWR in the harness or HO2S
    Water in the harness connector
    Open/shorted HO2S circuit
    Corrosion or poor mating terminals and wiring
    Damaged HO2S
    Damaged PCM
    Fuel System:
    Excessive fuel pressure
    Leaking/contaminated fuel injectors
    Leaking fuel pressure regulator
    Low fuel pressure or running out of fuel
    Vapor recovery system
    Induction System:
    Air leaks after the MAF
    Vacuum Leaks
    PCV system:
    Improperly seated engine oil dipstick
    EGR System:
    Leaking gasket
    Stuck EGR valve
    Leaking diaphragm or EVR
    Base Engine:
    Oil overfill
    Cam Timing
    Cylinder compression
    Exhaust leaks before or near the HO2S

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  • Medium-star Best Answer
    December 19, 2011, 17:26

    P1151 Lack of HO2S-21 Switching, Sensor Indicates Lean (Bank 2)Possible Causes Setting Conditions
    •Check for air leaks after the MAF sensor mounting location
    •Check for air leaks in the EGR system and in its related hoses and/or valve
    •Check for air leaks in the PCV system and in its related hoses and/or valve
    •HO2S connector is damaged (check pins for damage, and for moisture)
    •HO2S signal circuit open, shorted to ground, shorted to voltage
    •HO2S has failed (it may be contaminated with fuel, silicone or water)
    •Low fuel pressure or vehicle driven until it was out of fuel
    •Vacuum hoses leaking and/or damaged
    Engine running in Closed Loop; and the PCM detected that the Bank 2 HO2S-21 signal was less than 0.450v. In this case, the PCM is "correcting" rich for an overly lean condition.

    This code sets in 2 Trip(s).
    This code will turn on the MIL (Malfunction Indicator Lamp)

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