Question about 2000 Ford Expedition

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Service engine soon light is on. Have already replaced downstream oxygen sensor, as code # 174, (lean burn), indication on egine code. Should I replace all oxygen sensors?

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  • Anonymous Mar 21, 2014

    check egine light came on ran code is it easy to change



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Hi, no, don't do that. The code 174 indicates a vacuum leak--not a bad sensor. The leak can be anywhere downstream of the mass airflow sensor on the inlet pipe. Sometimes the rubber pipe itself tears/cracks, or maybe there is a loose vacuum hose or a torn brake booster diaphram. Check all the hoses attached to the engine intake manifold for a leak at either end or in between.
If all hoses are good, next check the intake manifold askets for leaks. Get yourself a can of carb cleaner and start the engine. Spray the gaskets all around. If the engine speed changes, you have a gasket leak--replace the gaskets. Since you have a code 174 and NOT a code 171, this is the most likely cause of the problem, because only the rigt bank is running lean. Be sure to check the gaskets on that passenger side carefully.
Last of all, if all that was good, check to see if your EGR valve is stuck open. I have pasted instructions for removing the valve below (from Please let me know if you have questions and thanks for using FixYa.

EGR valve R&R.

  1. Disconnect the negative battery cable.
  2. Remove the vacuum hose from the EGR valve.
  3. On the 4.6L engine, remove the nut and the brake booster bracket.
  4. Service engine soon light is - jturcotte_117.jpg
  5. On the 5.4L engine, remove the DPFE sensor retaining nuts and place the sensor to the side to allow access to the EGR tube.
  6. Disconnect the EGR valve-to-exhaust manifold tube from the EGR valve.
  7. jturcotte_118.jpg
  8. Remove the EGR valve mounting bolts, then separate the valve from the intake manifold.
    1. jturcotte_119.jpg
  9. Remove and discard the old EGR valve gasket, and clean the gasket mating surfaces on the valve and the intake manifold.

To install:
  1. Install the EGR valve, along with a new gasket, on the intake manifold, then install and tighten the mounting bolts.
  2. Connect the EGR valve-to-exhaust manifold tube to the valve, then tighten the tube nut to 25-35 ft. lbs. (34-47 Nm).
  3. Connect the vacuum hose to the EGR valve.
  4. On the 5.4L engine, install the DPFE sensor.
  5. On the 4.6L engine install the brake booster bracket and the retaining nut.
  6. Connect the negative battery cable.

      Posted on Jan 03, 2011


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      What does code p1131 mean on a 2001 ford taurus

      P1131 Ford
      P1131 Ford - Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 1

      Repair Importance Level: 3/3

      Repair Difficulty Level: 2/3

      Forum Code

      Possible causes

      - Faulty Oxygen Sensor

      - Vacuum leak affecting bank 1 only

      - Fuel injector problem bank 1

      - Check for cylinder misfire on bank 1

      - Engine mechanical condition

      Tech notes

      Though the Oxygen (O2) sensor, the Engine Control Module (ECM) has detected a lean system, which means that there is either not enough fuel or and excessive amount of air in the system. Start by checking for vacuum leaks.

      When is the code detected?

      The Engine Control Module (ECM) detected bank 1 oxygen (O2) at its lean limit

      Possible symptoms

      - Engine Light ON (or Service Engine Soon Warning Light)

      P1131 Ford Description

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

      Read more:

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      Replaced bank 1 and bank 2 downstream oxygen sensors on 2004 5 speed automatic diagnostic code still says not working

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      Check your work for vacuum leaks,can't have any

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      The oxygen content of the exhaust affects the O2 sensor resistance. This resistance produces a counter voltage on the reference/signal wire that the PCM will use to analyze oxygen in the exhaust. Lean exhaust produces low voltage, while rich exhaust produces high voltage. The oxygen sensor is capable of varying between 0.9v (rich) and 0.1v (lean). Once the engine reaches closed loop, the O2 sensor should begin switching rapidly between rich and lean voltages 2-3 times per second. If for some reason the O2 sensor doesn't switch properly or "sticks", P0154 may set. This code indicates the O2 sensor isn't operating.

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      P1151 = Lack of HO2S21 switch - sensor indicates lean, ( could be up, or downstream heated oxygen sensor ) " Downstream ", meaning after the catalytic converter.

      PO174 = System too lean, ( bank 2 ) The fuel/air mix ratio is bad.

      These DCT codes are generally caused by a problem with the emissions system. The following items are a few of the most common items to trigger those codes.

      1. Dirty air filter. ( very common )
      2. Faulty idle air control valve. ( common )
      3. MAF, ( mass air flow ), sensor. ( very common )

      All 3 of the above can prevent the onboard computer from determining the proper fuel/air mix ratio.
      The oxygen sensors measure to insure the fuel/air mix produces maximum power with minimal emissions.

      I hope this helps you.
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      P0174 System too Lean (Bank 2) - Read Our Article On Oxygen Sensor Codes For Help With This Generic Check Engine Light Code
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