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Discussion Starter #1
Funny Outside Temperature Quirk -

1996 E39 520i M52B20 Europe

1996 E39 520i M52B20 Europe

Hello all, not an important thread, just asking if anyone else has the same quirk:

The outside temperature that shows on the instrument panel sometimes becomes too low for real possible temperature: sometimes I turn on the car in the morning and it shows -15 degrees (or even lower) outside temperature which is simply impossible.

I chalk this off to a digital runaway error where the "computer" keeps adding minus temperature due to some part of the sensor or the digital system that will run away and instead of stopping at a temperature it keeps subtracting. This reminds me of the Patriot Missile digital computer that had a similar runoff error that was detected in the First Gulf War where missile would miss the target due to an error in the way the digital system was "written", even though it probably was not a normal "computer" like the laptops we have but a digital sequential computer. So the missile would constantly "add" distance to the target and miss it due to "digital run away". I don't remember the exact details but anyone can google it, I studied this case-study before. Could also be some "errant voltage" going around.

Anyways that is all irrelevant and I'm not trying to disctract you or waste your time from my simple simple question which is:

Has anyone else had this happen, and has it become worse to the point you needed to replace it?

I don't mind this quirk at all, and the moment you switch the car on, it starts slowly to climb up to normal temperature, which means the system is well built in the way it forces the temperature to climb or decrease slowly so that transient low temperatures dont show up misleading you (sometimes you drive through a patch of very low temperature that only affects a few hundred yards of the road you are in.

So it slowly goes back to normal temperature and always read good temperature once it is on.

I'm positive this has nothing to do with the engine management temperature that is probably separated from this ambient temp sensor.

my only question is again:

Has anyone else had this happen, and has it become worse to the point you needed to replace it?
 

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Wingnut
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thats an indication of a bad sensor, not a digital component issue, the OAT sensor is wired direct to the cluster, it is a buffered signal, like most others on this car, if replacing the sensor, disconnect the battery then reconnect after 20 secs or so, so that the cluster makes a new initila reading. the OAT sensor is just a plain ol NTC thermistor.
 

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Ditto mattmar1. See the info about OUTSIDE temperature (aka the ambient temp sensor) below. When it is not reading correctly...it affects the operation of other systems that require the ambient temperature (the IHKA control panel, heated mirrors, heated washer nozzles, etc).

 

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Discussion Starter #5
thats an indication of a bad sensor, not a digital component issue, the OAT sensor is wired direct to the cluster, it is a buffered signal, like most others on this car, if replacing the sensor, disconnect the battery then reconnect after 20 secs or so, so that the cluster makes a new initila reading. the OAT sensor is just a plain ol NTC thermistor.
I will look into replacing it in the future then. Should be easy and cheap?
 

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I have the automatic air control which also has a photo electric sun sensor apart from that instrument cluster sensor?
The little photo sensor on the front of the IHKA control panel (your auto air control)...located in the lower right vent opening...is for ambient lighting only. If your e39 has a solar sensor that is connected to your IHKA...it is located on the top center of your dash near the windshield. :)


The yellow arrow below is pointing to the IHKA's ambient light (photo) sensor:


The pics below are the e39's solar sensor (if you have one). If you don't have the IHKA w/MAX button, then you don't have the solar sensor:






 
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