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Location of Temperature Sensor

Discussion in 'Gen 3 Prius Technical Discussion' started by almhath, Aug 29, 2014.

  1. almhath

    almhath Junior Member

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    Hello,

    Out of curiosity, where is the temperature sensor on my Prius, 3rd gen?

    I'm wondering when it's more accurate: when I'm driving in the shade, or driving in sunlight...

    Thank you
     
  2. maurices

    maurices Member

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    It is behind the front bumper. As long as the car is moving (air flowing over/under the vehicle) accuracy will not be affected by sun, clouds or night/day.
     
  3. almhath

    almhath Junior Member

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    Okay. So if the pavement is hot, then the temperature may be reported a degree, maybe, or so, above ambient?

    This question does not matter in my life. I'm just someone who likes to learn things. My good, ole husband did encourage that.

    Thank you.
     
  4. jdcollins5

    jdcollins5 Senior Member

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    If you are parked then the hot pavement can increase the temp by several degrees. I have seen it as much as 5 degrees higher in the asphalt parking lot at work.

    As stated above, after you get moving the temp should correct to true ambient.
     
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  5. vito.a

    vito.a Junior Member

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    Also, if you go through a car wash the temp drops 20 degrees for 10-15 min.
     
  6. xliderider

    xliderider Senior Member

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    Driving over hot pavement/asphalt will report higher temperatures due to convective heat rising up from the hot surface. In my experience, it's a degree or two where I live. YMMV

    SCH-I535
     
  7. almhath

    almhath Junior Member

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    Right. "Ambient" air temperature is a good, yet imprecise term, because the air temperature, like everything else in nature, varies. It will be affected by the temperature of things around it, including the road, the air, including as compared to the adiabatic lapse rate ... everything.

    If the road is, say, 90 degreees, and the ambient air at shoulder height is 80, then the air temperature will vary between very close to that 90 down to that 80... If there is a temperature that day, and the air is actually getting warmer as you go higher (to some altitude), then in that same example, the air may be close to 90 at the road, cool as it distances from the road, then warm as it goes up with the temperature gradient...

    More usually, though, I'd think that, in this example of temperatures, at 18" off the road, the ambient air temperature for that altitude off the hot road could easily be an 85 or so, guessing. It would vary depending on a lot of things---

    The temperature of the objects around the temperature sensor will also affect its readings, including its bracket, the bumper...

    Moving is good, though, as the car, itself, the way it pushes the air as it moves through it, and the way the air will curl around features of the car like the bumper...will mix the air up and affect the temperature.

    Just mixing in ideas, looking at the issue.

    Overall, I do believe the temperature will vary on my indicator depending on things other than the ambient air temperature at the 18" of the sensor, including such things as the car wash mentioned, the temperature of the road, whether moving or sitting in shade or sun, clouds or not, the direction and speed of the relative wind, the inversion and/or lapse rate...

    I better stop before I think this is important. Maybe I should have a beer---which I would probably do, if I liked it at all.

    But thank you all for your good info.
     
  8. IanIanIanIan

    IanIanIanIan Member

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    And where is the cabin temperature sensor?
     
  9. jdcollins5

    jdcollins5 Senior Member

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    If you will read the entire thread you will find your answer in post #2.
     
  10. IanIanIanIan

    IanIanIanIan Member

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    Please re-read my question more carefully.
     
    #10 IanIanIanIan, Sep 1, 2014
    Last edited: Sep 1, 2014
  11. jdcollins5

    jdcollins5 Senior Member

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    Sorry, cabin temp sensor is under center console.
     
  12. RRxing

    RRxing Senior Member

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    The cabin temp sensor is located behind the blank switch plate (or switch, depending on model) by your right knee. There are openings just underneath the switch that you can feel with your fingers. This is where the air temp is sensed.
     
  13. jdcollins5

    jdcollins5 Senior Member

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    The Repair Manual shows in below the center console, not by your left knee.
     
  14. RRxing

    RRxing Senior Member

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    The "No. 1 Switch Hole Base" is located by your right knee, not below the console. The repair manual is just showing all of the center console pieces that have to be removed in order to access the Switch Hole Base and the temperature sensor. If you put your finger underneath the switch hole base you will feel the slots where the air temp is sensed.
    Room Temp Sensor.PNG
     
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  15. jdcollins5

    jdcollins5 Senior Member

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    Thanks for setting me straight on this location. I would have never have guessed with having to remove all that is necessary that the sensor is actually located behind the Switch Hole by your right knee :). I have never noticed the vents below the switch hole.
     
  16. RRxing

    RRxing Senior Member

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    No problem. I just hope I never have to replace the sensor. :eek:
     
  17. jdcollins5

    jdcollins5 Senior Member

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    Isn't that the truth! The interesting thing is I removed the blank switch cover and you can see the connector harness and you can see the sensor through the vent slots. It is right there at your fingertips.
     
  18. Jeffrey Jessup

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    May be off subject as to outside air temp location but... The last time I had the dealer wash my car was the first time I noticed the affect on the temp reading. It wasn't the first time they had washed the car since it had just had the 15k maint. but when I left the lot I immediately went back and told them they had messed up the temp sensor. They told me it was normal for a wash to do that but since that time it just seems like it is always inaccurate. I had always admired how close to the reported (weather channel) temp. it always was but now it seems to take several miles of driving (15+) to even approach that temp. after leaving my garage. It may be 95F outside but when I pull out it will be reporting 72F on the dash. It will gradually raise to maybe 81F after several minutes on the freeway and if I drive for 20 minutes or more it may get within 5 degrees of the actual temp.. I'm sure it was never this inaccurate before but have no proof and dealer isn't concerned. I was worried that this inaccuracy could be feeding into some info one of the computers uses that may relate to fuel air mixtures or something smog related. Probably just being paranoid .
     
  19. jdcollins5

    jdcollins5 Senior Member

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    That is unusual. I have gotten mine wet at car washes or driving through rain puddles but as soon as it dries out it goes right back to being accurate again.

    The only thing that I have seen the ambient sensor used for is the Climate Control System. According to the Repair Manual it uses the ambient temp sensor, the cabin temp sensor, and the solar sensor on top of the dash in its Fuzzy Logic calculations.

    If the car is still under the 36k mile warranty I would push the dealer to replace it. If out of warranty the sensor is located behind the front bumper and in front of the AC condensor coils. It is easy to get to and change and is inexpensive.

    I have not seen anything on it being used for the engine or emissions control.
     
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  20. RRxing

    RRxing Senior Member

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    And here's the kicker - the various temperature sensor settings are dealer-adjustable.

    AC Temp Shift.PNG
     
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