Calibrating Interior/Exterior Temp sensors

[AVC]

My exterior (outside) temp readout is 3 to 4 degrees HIGHER than actual temp. Most vehicles have some method to adjust that temp readout by making offset adjustments. Anyone come across a "hidden menu" to do this, or found this section in Forscan? I looked through Forscan for about 10 min and Got a bazillion hits on temp, which got tedious quickly.

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[srfdude44]

My exterior (outside) temp readout is 3 to 4 degrees HIGHER than actual temp. Most vehicles have some method to adjust that temp readout by making offset adjustments. Anyone come across a "hidden menu" to do this, or found this section in Forscan? I looked through Forscan for about 10 min and Got a bazillion hits on temp, which got tedious quickly.

Not trying to be a dick, what means do you have that tells you the readout is erroneous? Manufacturers use a thermocouple setup, which generally are quite accurate. The placement in the car is usually a problem, if the sun is hitting the general area of the car where said thermocouple is, it will read somewhat high. After driving a bit, normally the reading will come close to reality. IF you are comparing to a mercury type readout, well then.......

 

[AVC]

Hey Dick , I have a quick acting thermocouple meter, that I know to be +/-1% over a fairly wide range. which I can place outside the window in the air stream to monitor temp.

As I have a freeway commute, I've taken readings in Winter, Summer, sunny days, cloudy days. Vehicle pretty consistently *reads* 4F or so high, from about 15F to 110F.

Manufacturers typically use a NTC resistor in a plastic housing, rather than a thermocouple. The NTC isn't usually carefully binned by the supplier for these applications, nor are they "calibrated" at the Ford factory, per say. They depend on the "average" sensor to be within +/- x% of dead nuts.

1st step is to reset the learning algorithm for the PCM and see if that fixes the offset.

2nd step would be to determine the sensor resistance for at least two known temps (say 32F and 100F). determine if a small inserted series resistance would shift the curve colder to make the sensor report +/-1F of nominal over that range.

 

[oysterville]

Not trying to be a dick, what means do you have that tells you the readout is erroneous? Manufacturers use a thermocouple setup, which generally are quite accurate. The placement in the car is usually a problem, if the sun is hitting the general area of the car where said thermocouple is, it will read somewhat high. After driving a bit, normally the reading will come close to reality. IF you are comparing to a mercury type readout, well then.......

 

[srfdude44]

Great analysis! I hadn't looked into auto sensors for a long time, I defer to your more current knowledge!

 

[FischAutoTechGarten]

My exterior temp has been stuck at 52degF for 3 days.... It was over 85 degF here yesterday... So need to research what's going on with that..

 

[AVC]

My exterior temp has been stuck at 52degF for 3 days.... It was over 85 degF here yesterday... So need to research what's going on with that..

It's in denial--85F on Dec 23 does not pass the rational part of the algorithm.

 

[FischAutoTechGarten]

It's in denial--85F on Dec 23 does not pass the rational part of the algorithm.

Except that my truck was born in Hermosillo... It understands the winter temps here in the Sonoran Desert...

 

[AVC]

So, I noticed a week ago during a recent cold snap (25F) that the outside temp reading was oddly spot on. I have been monitoring it since, where the ambient was 54, then 63 and yesterday 74, and again spot on. Go figure...no over-air updates, or any other attributable reasons why it is suddenly accurate, rather than reading 4 to 5F higher than actual, as before.

 

[HeyBales]

There is a PID for it adjusting itself.

And I can see it could pull from either a start up Engine Coolant Temp reading, or a 12V battery temp reading, and on hybrid a startup HVB temp reading
Since those should match the ambient temps. I'm betting the programming logic isn't great though - like you can't do it on each startup, only when truck has been off for so many hours.

Sadly those ECT & HVB Temp don't match in the morning, ECT is higher - so if the ambient temp is being adjusted, I'm not sure to which one, but it seems to be pretty decent.

There is a Forescan Lite, so probably exists in full program - to reset that module and offset - let it relearn.

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