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I have a 2001 Audi S4. Last fall, I had maintenance performed on my car, and the shop accidentally, cracked my front fender. They told me about it and replaced it without any issue. However while replacing it, they took off and put back on my front bumper, where my ambient (outdoor) temperature sensor is housed. But they forgot to replace the sensor in the bumper, and it remained dangling below the undercarriage, and eventually was torn off while driving.

I did not notice anything incorrect for quite some time, but I started to realize that whenever it was raining (or the roads were wet), the temperature sensor dropped about 3F degrees per second, reaching -58F.

While not a big problem, this affected the heating and air conditioning air temperature. I started using a new shop that specializes in Audi's that is fantastic, and found the problem, and replaced the sensor and its wiring. The sensor now works fine in the rain.

However the sensor does not work all the time. Sometimes I will be driving, as I did recently from Durham, NC to Washington, DC, and between 2-3 hours into the drive, the temperature sensor drops from the current temperature of 80F to -58F, and then corrects itself, slowly going from -58 to the outside temperature. This takes ~6 minutes. A few minutes later, it does it again.

It only does this complete cycle twice. I am thoroughly confused on what could be happening. It stops working without any change in temperature or the weather. Any suggestions on how to resolve this weird outdoor temperature sensor issue?

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up vote 2 down vote accepted

Sounds like one of two scenarios depending on the design. -58 is the lower limit and happens whenever the sensor has no connection, or a direct connection.

The first step is to unplug the sensor and look at the temp if it goes to -58 then you have a loose or open connection somewhere between the sensor and the computer. If when you unplug the sensor it goes high like 130 then you have a wire grounding out somewhere between the sensor and the computer.

Either of the conditions is intermittent in your case which makes it more difficult to troubleshoot.

Visually inspect the wires and connectors from the sensor to as far back as you can follow them. The most likely place is in the area of the former damage.

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I had to replace the sensor. Now, however, my temperature gauge drops from the current temperature to -58 whenever I'm driving for about 2.5 hours. It will cycle down and up a few times, and then stabilize. Very strange. On longer road trips, it happens more frequently. –  Brian Aug 9 '11 at 11:48
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