Outside temperature sensor

Discussion in 'Generation 1 Prius Discussion' started by Itsmeonprius, Nov 27, 2019.

  1. Itsmeonprius

    Itsmeonprius Member

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    I've noted my temperature reading on the touchscreen gets higher and higher the longer I drive. And it certainly isn't 21°C here in drizzly Scotland at the mo!

    So I'm thinking the sensor has either fallen into a hotspot or it's just starting to give up.

    However, where is it?

    Keith

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  2. bisco

    bisco cookie crumbler

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    it is likely under the front bumper area, but i don't have a gen 1
     
  3. mroberds

    mroberds Member

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    It's behind the front bumper, but in front of the radiator and condenser assembly. I think I've seen it before, but I've never had to work on it; if I remember right it's close to the centerline of the car. You can probably see it by either opening the hood and looking in through the "nostrils" and down, or by taking off the splash shields under the trailing edge of the front bumper and looking up. The factory manual says "remove front bumper" to change out the sensor.

    The wires show up at pins TAM and E2 of the "ECM". With the key on, at those pins, you should have 1.35-1.75 V at 25 C / 77 F, or 0.85 - 1.25 V at 40 C / 104 F. Right at the sensor, with it unplugged, you should have 1.6-1.8 kohms at 25 C / 77 F, or 0.5-0.7 kohms at 40 C / 104 F.

    The only thing like that mine has ever done: when I park it outside in the summer for a while, and then get in the car and start it, the reported temperature is maybe 5 or 10 F (basically, 2.5 to 5 C) higher than what I think the ambient temperature is. After I drive the car for about a mile or so, the reported temperature decreases to something more reasonable. I think the sensor is accurately reporting what it "feels"; radiated heat from either the engine or the pavement, or just the sun shining on the front bumper, raises the actual temperature behind the bumper a little bit. Driving gets enough ambient air blowing around in there to lower the temperature again.
     
  4. Itsmeonprius

    Itsmeonprius Member

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    Thanks for the extensive information. I'll check through it when I get back from holiday. The temperature rises as I drive which I found strange. Normally if this type of sensor fails it just fails and defaults to a max temp. So it could be that its fallen off and touching the radiator hence the slow rise in temperature maybe. That's a theory and once I get into it I'll report back what I find.

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