2018 peterbilt 567 ambient air sensor?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by mixingconcrete, May 18, 2022.

  1. mixingconcrete

    mixingconcrete Light Load Member

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    Hello we are having code spn 171 fmi 2 on and we replaced the driver mirror harness with sensor and the door harness and code is still active. Is there more than 1 ambient air sensor? Does the intake manifold temp sensor have anything to do with this?
     
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  3. Another Canadian driver

    Another Canadian driver Heavy Load Member

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    Code : Spn 171 Fmi 2
    Ambient Air Temperature Not Plausible: Ambient Air Temperature Data Erratic, Intermittent Or Incorrect;
    Ambient Temperature Sensor Data Erratic
    I'm not a tech. I think it maybe a 5V sensor power supply issue.
    That voltage should have been checked first.
    Recommended:
    Check the voltage, the sensor, the connecters and harness.
    1 Ambient Air Temperature sensor only on this truck.
    Good luck.
    Let us know if it helped. Or not.
     
  4. mixingconcrete

    mixingconcrete Light Load Member

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    thanks for the reply but yes we have 5volts going to it, its just weird because it shows the outside temp on the dash so it seems like its working but the check engine light is on and it started to deratw because it cant do full regen im guessing
     
  5. Another Canadian driver

    Another Canadian driver Heavy Load Member

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    Do you have any other fault code that may cause the de-rate?
    Can the tech try to reset first all codes active and inactive and see what it does?
     
  6. mixingconcrete

    mixingconcrete Light Load Member

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    Thats the only code on, tried resetting and now its a permanent code
     
  7. Another Canadian driver

    Another Canadian driver Heavy Load Member

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    I
    The sensor should feed a reading into the ECM.
    Is it possible that a connector or a wire is interrupted going from the sensor to the ECM?
    Normally is checked with a multi tester set on Ohms
    with batteries disconnected to cut power to the ECM.
    While firmly shacking the harnesses to look for bad wiring or just connectors.
    All connectors should be visually inspected then cleaned up with a solution.
     
  8. Tigerfishinc

    Tigerfishinc Light Load Member

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    The ambient temp sensor - check near the intake charge pipe - it communicates with the ecm - controls/ feedback the fuel pressure sensor - assuming this is an isx
     
  9. mixingconcrete

    mixingconcrete Light Load Member

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    we tried to inspect all the wiring and plugs and everything looks good. Im kind of thinking maybe theres another ambient air sensor somewhere on the engine
     
  10. mixingconcrete

    mixingconcrete Light Load Member

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    its a paccar mx13 and i was thinking maybe theres another ambient air sensor on the engine because the code it says component (engine)
     
  11. spsauerland

    spsauerland Road Train Member

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    MX-13 uses mirror as ambient air temp sensor. The humidity sensor does also read turbo compressor inlet pressure, temp, and relative humidity. Need to hook up to a good scanner or Davie.
     
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