outside air temp and auto lights

[swieck]

I'm getting false readings on my external air temp. Anybody having or had the same problem? I'm guessing sensor problems, whatcha think ?? My auto headlights also stay on for quite sometime after I back out of my garage into broad daylight. Another sensor problem maybe ??? I'm heading back to the dealer next week with these complaints, so any insight would be greatly appreciated. Many Thanx.

[sidejam]

Oddly enough, I also have a problem with my outside air temperature reading...
For starters, I wish I knew where that sensor was.

[Rob the Elder]

The DIC does NOT show the current, real time outside air temp. If you do a little research you will see that it uses an algorythm and a time constant so the temp readout on the DIC always lags the actual external air temp and it will not react to instantanious short term changes in outside temps. It is not broken its working the way it is designed to work

[Rick Tinley Park]

Temp sensors take time to react, also how much is the temp off -- if it is 3-4 degrees it is most likely correct if you are comparing it to "bank" temps etc. Temp will vary 5-6 degreed just 100 feet apart.
Headlight sensors take about 30 seconds to react to daylight.

[Bogie]

You need to give us some numbers and times to work with.

Although the temp does use an algorithm, I've concluded it doesn't actually work the way it was designed in some instances. The algorithm is supposed to account for heat build up, and only go down until proper air flow exists (as a function of speed). I've noticed the reading will continue to be taken and stored even when the vehicle drops below the designated speed. This tends to skew the reading high when going slow or starting after a stop.

[gadget]

The Sensor is on the left side of the car behind the front bumper in the engine compartment. I don't believe there is any type of algorithum there would be a sample rate which would be the rate that the DIC polls an analog to digital converter. The rate of change would be the rate that the thermistor being used as a sensor reacts to a change in temperature.

[Bogie]

Here's a better description:

DIC Temperature: Mussings of an Engineer

[gadget]

Originally Posted by Bogie

Here's a better description:

DIC Temperature: Mussings of an Engineer

How do you know this algorithum exists? I can tell you from experience why the sensor is where it is.

1. Solar: The sun cannot directly hit the sensor if it does you will not read air temperature
2. Water :Moisture on the sensor will give you what is known as Wet Bulb this factors in the effects of humidity.

3. Wind : direct placement on the outside of the venicle will factor in the cooliing effect of wind chill which varies with the speed of the car and humidity.

To get a true outside air temperature the sensing bulb or in this case RTD sensor has to be in still air unaffected by any of these items. Unfortunately that is nearly impossible to do on an automobile.So the placement of the sensor was selected to minimize all of these factors. Will it pick up some heat soak from the engine when the car is not moving. Yep sure does! But there are no perfect solutions.

As to whether or not there is an algorithum used in the calculation. I do not know for certain.
I have told you electrically how the sensor works. I deal with these all of the time and it is my guess that an RTD (Resistance temperature Detector) that was relatively slow was selected to keep the temperature display from making violent swings on the changes that are seen in an automobile.

I have tried and seen programmers try to use algorithums to correct temperature and pressure readings in large air systems and it usually ends up in certain conditions making the readings even farther off. Changing the sample rate that the computer or display polls the sensor is somewhat usefull in many applications. I have also tried referencing tables stored inside the automation processors memory to correct certain readings however this takes up lots of memory inside a small processor and generally the table can never be made large enough to have a good effect and take up a great deal of the processors time to use.There are more important things to do with processing power in a small controller than just to read or calculate outside air temperature.
Any programs that are written for small controllers like the ones that are in use in the Sky are kept as small as possible to keep processor and buss usage as low as possible.

[Bogie]

Originally Posted by gadget

How do you know this algorithum exists?

There is a TSB out (I don't know the number), but here's an excerpt (all I have) of the TSB text. I think I extracted this text when someone else posted on the boards; don't remember when:

Condition/Concern:
Some customers might complain about the outside temperature display reading is inaccurate at times.

Recommendation/Instructions:
Outside Air Temperature Display Operation

The outside air temperature algorithm uses 3 pieces of information, outside air temperature data, vehicle speed and time the engine was turned off. When the engine is first started, the algorithm looks at how long the engine was off and if the outside temperature is lower than the last reading taken during the previous ignition cycle to determine if a new outside temperature reading should be taken. If the engine was off long enough or the current outside air temperature is cooler than the stored value, a new outside temperature reading is taken and displayed in the cluster. If the engine was not off long enough or the current outside air temperature is higher than the stored value from the previous ignition cycle, then the last stored value (outside air temperature) taken will be displayed. The outside air temperature will continue to be updated every second as long as the outside air temperature is the same or cooler than the previous reading.

Once the new outside air temperature reading exceeds the previous temperature & the vehicle is traveling less than 18 mph, the displayed outside air temperature will remain at its last value. Once the vehicle speed exceeds 18 mph the displayed outside air temperature will be updated. If the speed drops below 18 mph, the outside air temperature will freeze at its last value.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

[swieck]

I am pretty sure the sensor for the air temp is less than even being close to accurate. example would be the other day it registered 66, it stayed at that reading all day. It was in the 80's as confirmed by all sorts of sources. My wifes chrysler 300 air temp sensor updates its readings frequently and seems to be VERY close to actual temps.The issue with the auto lights is similar. The lights come on in the garage when it start the car, after leaving the garage and driving in daylight the lights will stay on for quite some time, 5-10 miles of driving before shutting off. Again, I have two other vehicles that have auto lights and they shut off before I reach the end of the driveway. So would I be correct in assuming that these sensors are faulty? I appreciate everyones input, thanks much.

[gadget]

Originally Posted by Bogie

There is a TSB out (I don't know the number), but here's an excerpt (all I have) of the TSB text. I think I extracted this text when someone else posted on the boards; don't remember when:

Interesting to know

This is a good example of errors introduced by using Algorithums:
"The outside air temperature will continue to be updated every second as long as the outside air temperature is the same or cooler than the previous reading".

So if the true outside air temperature happens to be increasing at the same time this algorithum is running the processor will not recognize it.

That would explain why you have seen the car display 66 degrees F when the outside air temperature is closer to 80 degrees F
I have not payed constant attention to the temperature display in the Sky but have usually found it to be within 4 or 5 degrees of anything I referenced it to while the vehicle was moving.I will try to pay more attention to it

RTD sensors very rarely go bad.

[swieck]

Am I to assume that the sensors in my chrysler are of a different type inasmuch as they update the readings MUCH faster than the sky. Or possibly the skys sensors are of a lessor quatity ? I don't know..... If they all use the same technology then why the big differences in performance?

[gadget]

Originally Posted by swieck

Am I to assume that the sensors in my chrysler are of a different type inasmuch as they update the readings MUCH faster than the sky. Or possibly the skys sensors are of a lessor quatity ? I don't know..... If they all use the same technology then why the big differences in performance?

Apparently the way the processor is programmed to use the information it collects from the sensor.

[Rustyknight]

Originally Posted by gadget

Interesting to know

This is a good example of errors introduced by using Algorithums:
"The outside air temperature will continue to be updated every second as long as the outside air temperature is the same or cooler than the previous reading".

So if the true outside air temperature happens to be increasing at the same time this algorithum is running the processor will not recognize it.

That would explain why you have seen the car display 66 degrees F when the outside air temperature is closer to 80 degrees F
I have not payed constant attention to the temperature display in the Sky but have usually found it to be within 4 or 5 degrees of anything I referenced it to while the vehicle was moving.I will try to pay more attention to it

RTD sensors very rarely go bad.

If the car is going faster than 18mph it will update with the latest reading regardless if it is going up or down, the algorithums does not introduce errors it only tries to present the user with what it hopes is the best possible value when the car is first started but before adequate cool off time has elapsed or going less than 18mph (since in both case heat from the engine can skew the readings)

[JRinKY]

Rustyknight : If the car is going faster than 18mph it will update with the latest reading regardless if it is going up or down, the algorithums does not introduce errors it only tries to present the user with what it hopes is the best possible value when the car is first started but before adequate cool off time has elapsed or going less than 18mph (since in both case heat from the engine can skew the readings)

Correct.

For what its worth, whenever I have checked it, mine has always read what seemed to be the correct temperature.

Headlight control is time-delayed to minimize rapid cycling when going through shade, etc. So a 30 second delay is perfectly normal.

[gadget]

I watched mine all day yesterday when I got in it. It read the same temperature as the garadge and after 4 or 5 min of driving it was fairly close to the outside air temperature and stayed within a few degrees all day long.