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thermometer - slow responding


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9 replies to this topic

#1 jib

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Posted 15 May 2007 - 11:27 PM

I just started noticing a weird functioning of the LCD thermometer in my 02 Legacy GT. I park in an underground parking garage, which is usually cool. Today, when I got into the car it was reading 66°F, which is about right. It was 80°F outside, beyond the parking garage. 20 minutes and 15 miles down the road, the reading was still slowly rising into the mid ti upper 70's.

I had never seen it respond this slowly. The sensor (thermocouple) in front of the radiator, near the horn, is clean.

Any thoughts?

Thanks in advance,

Jack

#2 Legacy777

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Posted 16 May 2007 - 11:01 AM

Is this the only time it has happened, or is it happening again? Did you try turning the car off and on again?

#3 ferret

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Posted 16 May 2007 - 12:26 PM

Here's the writeup from the FSM for an 04:


The outside air temperature display system consists of an ambient sensor, the CUSTOM CPU and
a liquid crystal display installed in the combination meter. The ambient sensor detects the outside
air temperature using the built-in thermistor which varies its resistance according to change in ambient
temperature, and sends signals to the CUSTOM CPU.
As soon as the ignition switch is turned ON, the CUSTOM CPU compares the temperature data sent
from the ambient sensor with the one that was stored in its memory when the ignition switch was
turned OFF last time and it causes the lower of the temperatures to be displayed. However, if 60
minutes or more time has passed between the last turning OFF and the next turning ON of the ignition
switch, the temperature that is displayed is a sensor-provided temperature.
When the vehicle is running slowly, the heat released from the engine compartment raises the temperature
of the air around the ambient sensor and this affects the temperature data the sensor
sends to the CUSTOM CPU. The CPU then makes a special control using the vehicle speed data,
i.e., when the vehicle is running at a speed slower than 10 km/h, the CPU uses the temperature that
was detected during the most recent vehicle’s movement at a speed exceeding 10 km/h rather than


a temperature currently being provided by the ambient sensor.


#4 nipper

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Posted 16 May 2007 - 02:06 PM

Here's the writeup from the FSM for an 04:



The outside air temperature display system consists of an ambient sensor, the CUSTOM CPU and
a liquid crystal display installed in the combination meter. The ambient sensor detects the outside
air temperature using the built-in thermistor which varies its resistance according to change in ambient
temperature, and sends signals to the CUSTOM CPU.
As soon as the ignition switch is turned ON, the CUSTOM CPU compares the temperature data sent
from the ambient sensor with the one that was stored in its memory when the ignition switch was
turned OFF last time and it causes the lower of the temperatures to be displayed. However, if 60
minutes or more time has passed between the last turning OFF and the next turning ON of the ignition
switch, the temperature that is displayed is a sensor-provided temperature.
When the vehicle is running slowly, the heat released from the engine compartment raises the temperature
of the air around the ambient sensor and this affects the temperature data the sensor
sends to the CUSTOM CPU. The CPU then makes a special control using the vehicle speed data,
i.e., when the vehicle is running at a speed slower than 10 km/h, the CPU uses the temperature that
was detected during the most recent vehicle’s movement at a speed exceeding 10 km/h rather than



a temperature currently being provided by the ambient sensor.


Man thats complicated......

I have an aftermarket rear view mirror. i have been experimenting with where to put the sensor, and in all honesty, there is no place in a modern car that is exempt from the heat of the sun. There is also a lot of radiant heating from the road surface, and other cars.

It is really really hard to make one accurate all of the time. If its a cloudy day and your only the one on the raod, thats the time thats best.

Different manufaturers have tried many different places to mount the sensor (grill, outside rear view mirror, under the fender, engine air intake), none of them are perfect.

At best its just a referernce.

nipper

#5 Skip

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Posted 16 May 2007 - 02:42 PM

For my remote read thermo,
I mounted my
remote probe inside the front of the
drivers door jamb where the hinge
protrudes into the inner fender.

Back to the un-hijack

My 03 VDC seens to take about 5 to 10 min to read
true amibient temp.

The GL-10 I had was faster.
Old school??

#6 nipper

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Posted 16 May 2007 - 02:48 PM

hrmmmm door jamb .....


nipper

#7 jib

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Posted 16 May 2007 - 10:57 PM

The car was started and stopped at least once on that day and 15 minutes of run time was on the highway. I did not notice it today, but will have to check again tomorrow.

Thanks for the responses thusfar!

Jack

#8 Sweet82

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Posted 17 May 2007 - 12:06 PM

I've had the same complaint.

Subaru just sent another sensor unit.

It did the same thing.

My slow sensor was on the optional gauge pack in the center of the dash.
The one in the drivers instrument cluster works fine.

Glenn,
2001 Forester

#9 jib

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Posted 18 May 2007 - 02:52 PM

What do you mean "Subaru just sent another sensor unit."? Was it a recall or did you have to pay for it? If paid, what did it cost?

Do you have the part number?

Thanks,

Jack

#10 86BRATMAN

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Posted 18 May 2007 - 07:37 PM

Our 06 2.5i is slow reading sometimes as well. I'm not really to concerned to be honest. Its just another electronic device to go bad over time.




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