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Thread: Temperature shows -40 degrees on dashboard

  1. #1
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    Temperature shows -40 degrees on dashboard

    I've had this problem since I bought my car but the dealer said it would cost me 600$ to fix. Figuring its not hurting the cars performance, I let it be all these years. But I'm thinking it's either a simple sensor or temperature control? Or the thermostat?

    I got a check engine recently telling me that the thermostat needs changing, probably jammed open... But I really want to get to the bottom of the temperature reading -40 degrees on a beautiful sunny day.
    IG: ZeeZooM3


  2. #2
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    There is a outside temp sensor on the right side of the car, if you look at it from the front, you should see a little probe like device. I guess it will need changing. If your thermostat is bad, you should at least replace the water pump, but I recommend doing at least the water pump, radiator and expansion tank, they are going to fail anyway
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  3. #3
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    It's the outside temp sensor its shot, usually when they go they do just what you see and read -40 or whatever, replace it your self and save monies.

    Also while your at it, it's probably time for a cooling system overhaul, thermostat, pump, hoses etc.

  4. #4
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    Thanks for the replies. I'll look into the temperature sensor even though I still don't really know where it is unless I have a picture but I'll google it.

    My water pump went bad almost a month ago, almost destroyed my engine from overheating but thankfully I pulled over and shut it off in time, whew. Also, the radiator went bad 2 months ago, or a month before the water pump went bad.

    Basically I have a brand new radiator, expansion tank, water pump. My power steering fluid is leaking from the hoses under the resovoir though. It's a common problem, I just have to either change the hoses or tighten the rings with a screwdriver.

  5. #5
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    Behind the front bumper



    Behind this panel in the wheel well



    Right above #7 towards the front
    http://www.realoem.com/bmw/showparts...98&hg=41&fg=10
    Last edited by spoonerDee; 12-23-2011 at 08:22 AM.

  6. #6
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    Quote Originally Posted by ezbmr
    There is a outside temp sensor on the right side of the car, if you look at it from the front, you should see a little probe like device. I guess it will need changing. If your thermostat is bad, you should at least replace the water pump, but I recommend doing at least the water pump, radiator and expansion tank, they are going to fail anyway
    Left side. Drivers side.

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  7. #7
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    Took a look under my car and I've never realized that there is supposed to be a plastic cover there. Here are some pictures:

    http://img266.imageshack.us/img266/2187/downloadmx.jpg
    http://img542.imageshack.us/img542/8855/download1fw.jpg

    I don't have time right now to look for the wires for the sensor but I will when I get a chance. Instead of buying a new cover (both sides I presume), I though I would get the sensor from the nearby dealer and hook it up to the wires and hold it in place via zip ties or tape to the bumper or another solid space. Will that work?

    BTW the plastic cover where the sensor sits was long gone when I bought the car from the previous owner so don't think the tire touches the plastic at all, at least at the moment it doesn't.

  8. #8
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    The reason you don't have it is probably one of those screws got missing and then that cover came loose, when it does, it looks ugly so the PO must have tore it apart instead of fixing it. That issue can't cost $600! Just a replacement of the sensor will do.

  9. #9
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    I have a quick question because i feel that the mechanic I was talking to was trying to rip me off or was wrong about his assessment.

    My AC had not been working properly, spewing hot air in a few days even after I put fill it up with the AC fluid... after he checked for leaks and couldnt find any he asked if there is a message on my dashboard saying -40 which it has because I had an accident a few weeks back crashing into the back on another vehicle. He suggested that replacing the sensor will lead to an improved performance of the AC because they are connected. This feels like bulls***t, but I don't want to be aggressive in my expressions without verification... can someone help out?

  10. #10
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    Looks like you ask in the wrong forum, if your car is a built 2010 318i, it is not an E46, but 3-Series E90-E91 Sedan/Touring, 2004-2012.
    Shogun tricks and tips for the E32 series are HERE!

  11. #11
    Join Date
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    1999 E46 328i, 2002 E39

    Exterior Temp Sensor

    Quote Originally Posted by karimabdoun View Post
    I have a quick question because i feel that the mechanic I was talking to was trying to rip me off or was wrong about his assessment.

    My AC had not been working properly, spewing hot air in a few days even after I put fill it up with the AC fluid... after he checked for leaks and couldnt find any he asked if there is a message on my dashboard saying -40 which it has because I had an accident a few weeks back crashing into the back on another vehicle. He suggested that replacing the sensor will lead to an improved performance of the AC because they are connected. This feels like bulls***t, but I don't want to be aggressive in my expressions without verification... can someone help out?

    The -40 is an indication that there is an issue with the Exterior Temp Sensor. Probably open (could be either missing or defective) This sensor does indeed work in conjunction with the A/C system. You can easily replace the sensor yourself. It is located on the bottom of the plastic shroud just ahead of the drivers side tire. I accessed mine by removing the Air Filter housing box (2 - 10mm bolts and two flip clamps which hold the box to the MAF). When the Airbox is removed you can reach straight down and pull the sensor and wire from its mount by pulling it towards the front of the car. The sensor can be had online for about $14 bucks (URO Parts 65 81 6 905 133 Air Temperature Sensor)... Many people also replace the 2 wire connector (I got mine at Pelican Parts) for a few bucks since it can be corroded or missing. The wires that attach to it are Blue/Red(attaches to pin 1 on the connector) and Blue/Brown(Pin 2).

    Hope this helps...

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