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Here's an odd one.

I returned home from a long trip where the car was outside for about 10 hours. I parked the car in my garage. I have my garage heated to 48°F. After charging for about 3 hours, we decided to go out for dinner. So I unplugged, opened the garage door, powered up and the ERDTT came on immediately. The dash showed 17°F! As I said, the car was in a garage heated to 48°F for three hours. No way was it 17°F.

Even if it were encased in a block of ice, the thermostat should see no more than 32°F. So I'm wondering, could this be some delayed "memory" by the car of the outside temperature before I pulled into the garage? Could the thermostat be off/faulty (it seems reliable otherwise)? Or are the Volt space aliens messing with me?

I haven't had a chance to do more investigating, but it is curious.
 

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2 possible thoughts.

1. Sensor doesn't reset until a full charge is attained.
2. The sensor was submerged in a slurry of slush and salt that was actually at 17°F.
 

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I had that happen to me as well under similar circumstances. Our garage is usually around 58 degrees. I simply chalked it up to the thermostat having to reset itself *that is a guess of course*. It has never done that after charging overnight. But when it did happen, I was startled because of course I had the garage door closed!
 

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Mine did it as well, when I was playing with the OAT sensor, after it was unplugged it read -40, even driving around the block did not stop it. I put the key fobs in a metal box over night and by the morning it had reset. Not sure why it takes it's time.
 

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Here's an odd one.

I returned home from a long trip where the car was outside for about 10 hours. I parked the car in my garage. I have my garage heated to 48°F. After charging for about 3 hours, we decided to go out for dinner. So I unplugged, opened the garage door, powered up and the ERDTT came on immediately. The dash showed 17°F! As I said, the car was in a garage heated to 48°F for three hours. No way was it 17°F.

Even if it were encased in a block of ice, the thermostat should see no more than 32°F. So I'm wondering, could this be some delayed "memory" by the car of the outside temperature before I pulled into the garage? Could the thermostat be off/faulty (it seems reliable otherwise)? Or are the Volt space aliens messing with me?

I haven't had a chance to do more investigating, but it is curious.
The Temp sensor is not "as" active with ignition off as it is when ignition is on. It can take up to 5 miles of driving for the temp sensor to read actual ambient temp. sounds like normal operation to me
 

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Mine did it as well, when I was playing with the OAT sensor, after it was unplugged it read -40, even driving around the block did not stop it. I put the key fobs in a metal box over night and by the morning it had reset. Not sure why it takes it's time.
FWIW: After disconnecting B9 thus creating an open or max resistance, it will generally take around 1 1/2 to 2 Hrs for the Hybrid/EV powertrain control module 2 K114A to recal. and begin showing true temp on the center stack touchscreen again once B9 is reconnected. There will also be a non-CEL latching Ambient Air Temperature Sensor High DTC that will have to be cleared using an OBD-II tool.
 

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I agree that the sensor has a slow reaction time. I've notice that when I pull in or out of heated building it takes almost 5 minutes sometimes to show the actually temp.
I wounder if they are avg the data sample for some reason?
 

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That has happened to me a couple of times. Think it is a computer brain cramp. Always corrects itself after a minute or two of driving.
 

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So I too park my volt in my insulated garage but which is not heated. Poking my interest in the question I turned the volt on and its temperature for the room was 37. I then used a digital home monitoring thermometer and it said 38. So I drove the volt home yesterday in 25 degree weather temps, parked it immediately in the garage, plugged it in and never turned it on again until I went to check the room temp this morning. Not sure what that says in terms of other observations but it seems going through a full charge cycle at least the volt was keeping the temperature current. I doubt if it had the outside temp of 25ish from yesterday it could react to 37 that quick for the moment I turned it on. So I think if its working normally its ongoing. Comments? BTW 2014 volt.
 

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I agree that the sensor has a slow reaction time. I've notice that when I pull in or out of heated building it takes almost 5 minutes sometimes to show the actually temp.
I wounder if they are avg the data sample for some reason?
+1 on slow reaction time. Process control systems are not always real time. They sample at set intervals. Wait it out, after a minute, check it again. Should change over time if in a heated garage.
 

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It seems you've identified another "feature". My 2013 does the same thing. Garage heated to 45, outside temps around zero, pull in and park for an hour, car still thinks it's 5 degrees when I get in to drive. Overnight full charge never does that though. It always shows around 38 in the morning when I pull out. I assume that small difference is due to the garage thermostat being mounted on a warm wall and the Volt is closer to a cold garage door.
 

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I have a similar issue, discussed a bit here. I just had the sensor replaced yesterday and it's still behaving the same. Software bug? What bothers me is that it quickly and accurately reflects a dropping temperature but never the opposite.
 

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The displayed ambient air temperature sensor (AAT) is a "filtered" value. This is necessary to prevent "heat soak" from affecting the various devices that utilizing the data from the AAT (climate controls, powertrain controls, various thermal management systems etc etc) since the sensor is mounted out front near the radiator stack inlet. This prevents the vehicle from working with an unrealistically high value as radiated heat affects the sensor during short duration parking events. Typically instantaneous drops in temperature are immediately observed, however increases in temperature are "buffered" in software based on a real time clock (time since OFF power mode) OR until the vehicle reaches a minimum vehicle speed for a defined time period. Most all GM cars and trucks operate in this fashion.

However on the Volt this "normal" behavior can have an impact on the behavior of ERDTT under certain circumstances. (as Steverino has noted)

WOT
 

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The displayed ambient air temperature sensor (AAT) is a "filtered" value. This is necessary to prevent "heat soak" from affecting the various devices that utilizing the data from the AAT (climate controls, powertrain controls, various thermal management systems etc etc) since the sensor is mounted out front near the radiator stack inlet. This prevents the vehicle from working with an unrealistically high value as radiated heat affects the sensor during short duration parking events. Typically instantaneous drops in temperature are immediately observed, however increases in temperature are "buffered" in software based on a real time clock (time since OFF power mode) OR until the vehicle reaches a minimum vehicle speed for a defined time period. Most all GM cars and trucks operate in this fashion.

However on the Volt this "normal" behavior can have an impact on the behavior of ERDTT under certain circumstances. (as Steverino has noted)

WOT
Love it. Hearing this description makes me wish I was developing software/firmware (C or VHDL) for GM's plug-ins. I think I would enjoy it!
 

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Love it. Hearing this description makes me wish I was developing software/firmware (C or VHDL) for GM's plug-ins. I think I would enjoy it!
LOL Maybe...
But this example is perhaps a bit more intuitive than one might think, as after only 3 hours, chances are the true ambient condition outside the heated garage hadn't changed all that much in 3 hrs. So ERDTT was probably going to be necessary anyways.

WOT
 

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Just an FYI The outside air temperature that is accessed through the driver information center Trip/Fuel switch function. And shows the outside air temperature as a damped value. The time and rate of the temperature update is based on an algorithm in the instrument cluster. Factors such as last temperature reading, current temperature reading, length of time the vehicle was off, current vehicle speed, and the distance driven effect when the displayed temperature is updated. To get the vehicle to display the most accurate temperature faster, drive the vehicle. Constant moving traffic will update the display to the correct temperature more quickly than stop and go traffic. Hope that helps...
 

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In all cases other than EV that determines whether to run the ICE to generate heat, this is a good thing. Kinda like how the fuel level is now buffered. I remember the late 80s and 90s GM cars the fuel gauge would bob up and down. Now its a slow reaction. Unless you fill it up all the way, then for some reason it resets a lot faster.

Heat soak is definitely a problem where I live. Even with the "buffer" time, it still gives triple digits temps, even when it is only mid 80s out.
 

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Just an FYI The outside air temperature that is accessed through the driver information center Trip/Fuel switch function. And shows the outside air temperature as a damped value. The time and rate of the temperature update is based on an algorithm in the instrument cluster. Factors such as last temperature reading, current temperature reading, length of time the vehicle was off, current vehicle speed, and the distance driven effect when the displayed temperature is updated. To get the vehicle to display the most accurate temperature faster, drive the vehicle. Constant moving traffic will update the display to the correct temperature more quickly than stop and go traffic. Hope that helps...
FWIW: Doesn't necessarily apply if you remove B9 completely, i.e. create an open circuit. If the Volt is turned on w/B9 removed, the DIC will indicate -40C/F and an ERDTT even would occur almost immediately!;)
 
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