Outside temperature reading incorrect.

Discussion in 'Prime Main Forum (2017-Current)' started by Nancy S, Jun 20, 2017.

  1. Nancy S

    Nancy S Member

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    Trying to figure out if I've got an issue or just a dirty temperature sensor. I left my office's underground parking this afternoon and the initial reading was 93 degrees. Drove home 22 miles in verified 118 degree weather and the temperature only rose slowly up to 106 by the time I got home. As much as I wish it was only 106, I know the reading was off by 12 degrees. Could the sensor be dirty? Does anyone know where the sensor is located to check that idea?
     
  2. joachimz

    joachimz Senior Member

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    I was taking a trip this past weekend for ~ 45 min and it took at least a half hur for the display to catch up with the real outside temperature, seen this before in my Gen3 so am not worried ... i'm n to sure where the outside temp sensor is located
     
  3. Elektroingenieur

    Elektroingenieur Senior Member

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    I wouldn’t recommend any troubleshooting or repair for an error of less than 2% in absolute terms (|577.7 °R - 567.5 °R|/577.7 °R ≈ 1.77%), assuming the actual air temperature along your car’s route was really equal to the “verified 118 degree weather” you mention—which it probably wasn’t, if that was an official observation made at another time and place, rather than a calibrated thermometer near your car.

    Indeed, such an error falls within the tolerances given in Toyota’s Repair Manual (RM32D0U, available by subscription to techinfo.toyota.com), under Vehicle Interior: Heating / Air Conditioning: Ambient Temperature Sensor: Inspection, where this table appears:
    Code:
       CONDITION    SPECIFIED CONDITION
      ------------  -------------------
      10°C (50°F)     3.00 to 3.73 kΩ
      15°C (59°F)     2.45 to 2.88 kΩ
      20°C (68°F)     1.95 to 2.30 kΩ
      25°C (77°F)     1.60 to 1.80 kΩ
      30°C (86°F)     1.28 to 1.47 kΩ
      35°C (95°F)     1.00 to 1.22 kΩ
      40°C (104°F)    0.80 to 1.00 kΩ
      45°C (113°F)    0.65 to 0.85 kΩ
      50°C (122°F)    0.50 to 0.70 kΩ
      55°C (131°F)    0.44 to 0.60 kΩ
      60°C (140°F)    0.36 to 0.50 kΩ
    In the table, “CONDITION” is the actual ambient temperature, and “SPECIFIED CONDITION” is the resistance measured across terminals 1 and 2 of the ambient temperature sensor (thermistor assembly).

    Notice the broad ranges and how they overlap at higher temperatures. The sensor doesn’t need to be a precision scientific instrument, just accurate enough for the car’s systems to operate properly and to give the driver an idea of whether it’s cold enough outside for roadway icing; with these requirements met, the low cost, robustness, and simple wiring for a thermistor make it a good choice, even if more accurate measurements could be made with a thermocouple or resistance temperature detector.

    The Repair Manual also shows the sensor location, behind the front bumper on the driver’s side. The approximate location is also shown in Toyota’s Electronic Parts Catalog, in Figure 87-15, Heating & Air Conditioning – Control & Air Duct, as part number code 88790B.

    If you do choose to remove the thermistor assembly for inspection, remember to hold it only by the connector, not by the sensor itself. Disconnecting it for testing may also cause diagnostic trouble codes to be recorded, which would need to be cleared with Toyota Techstream or an equivalent tool.
     
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  4. bwilson4web

    bwilson4web i3 and Prime

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    It begs the question of whether the thermistor is behind the vanes or in an area of reduced airflow. But for $3-5, you can get a Harbor Freight thermometer and affix it to the outside, rear view mirror stalk so it can be read in the cabin. Just I'm not that curious about the error.

    Bob Wilson
     
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  5. bisco

    bisco cookie crumbler

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    i have the same problem in my pip. thermometer reads 86f in the shade, that agrees with the on line temp for the area. pull the car out of a 70 degree garage, drive 8 miles in 20 minutes, and it's only up to 77f.
    leave the car in the shade for an hour, it gets to 81f. drive home, another 20 minutes, 82f.
    there are many threads here, citing this problem, but no solutions.
     
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  6. mmmodem

    mmmodem Taste Tester

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    I find the temperature very accurate at least to my well calibrated "it feels like" index. The temperature reading does not always match what my phone or online says it is but I don't expect it to. My location on tarmac will undoubtedly be a different temperature than the beach running 100 yards parallel next to the road. The temperature reading in my car is ambient within minutes after exiting my warm garage.

    It looks like the sensor temp overlaps only occur at triple digits. Luckily that's rare where I live. The heatwave going on in the southwest? I think my location only got up to 95. The online temps said 105.
     
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  7. huskers

    huskers Senior Member

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    If you were your car would you want to admit it was 118 outside?
     
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  8. Nancy S

    Nancy S Member

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    Thanks for the information and insight. The slow rise in the temperature makes sense after I think about my experience on Monday. We went to the movies and got out about 5:30. The Prime had been sitting behind a building in the shade. The temperature read 118 (the high was 119) when I started it up.
    This morning I went out and started both cars to see what the temperature reading was. The Leaf read 93 degrees and the Prime 95 degrees but the Prime had been charging a few hours earlier.
    I guess the slow rise is probably normal for this car. My gen 3 and our old Lexus were pretty accurate after about 10 minutes. The Prime would take more than 45 to reach an accurate reading I guess. It's not that big of a deal and I'm not concerned about it. After all, when it's above 105, it really feel the same as 120 anyway....but it's a dry heat :cool:
     

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  9. Dale Leonard

    Dale Leonard Member

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    Run it through a car wash and see how long it takes to come back up.
     
  10. RRxing

    RRxing Senior Member

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  11. David Beale

    David Beale Senior Member

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    A "dirty sensor" won't affect the reading after a few minutes. As any Toyota tech. will tell you, "it's normal". ;)

    Oh, and unless they've moved it, the sensor is about half way up the strut under the hood latch.
     
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