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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 5 Series > E39 (1997 - 2003)

E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 10-20-2013, 11:17 PM
540IVincent 540IVincent is offline
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Location: San Ysidro, CA, USA
 
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Mein Auto: 1997 BMW 540I
Ambient Temp Reading Has Gone Nuts Unlike No Other I Have Read About

Hello All,
I have a 1997 BMW 540I and my dash reading for my ambient temperature is reading all over the place between -30 to -71 and I need help as my A/C will not work because of this. I have already repaired the ambient temp sensor wiring by soldering a new connector to the harness and installing a new OEM temp sensor so I know that this cannot be the issue. I even tried installing 3 other temp sensors that I know were good that came from friends cars, same crazy readings. Besides everything I have read the default reading for a shorted sensor is -40 or 122. I followed the harness the entire way and there are no damaged areas. I noticed that the opposite end of the harness to the temp sensor connects to a green colored connector that I think may be some kind of sensor that is attached to a tube leading to the A/C system just behind the p/s headlight, could this be the problem? What is this part called? Prior to the repairs I mentioned, my dash reading was -40 so I knew the temp sensor was shorted out and now after two days after the repairs and doing some driving it is -70. I drove through a large puddle of water and it dropped down to -71. Anyone have any suggestions as to what this could be? It is drving me crazy as everything else works on my car and I treat my car as if it were my first born. Has anyone else had a similar issue, what was the fix? Any adivse/help would be greatly appreciated. Thank you so much,

Vincent
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  #2  
Old 10-21-2013, 09:33 AM
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johnstern johnstern is offline
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Mein Auto: 2000 BMW 528iT/5, S/C
Don't know if you've read this but it might help.

http://forums.bimmerforums.com/forum...or-Replacement
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  #3  
Old 10-21-2013, 07:52 PM
540IVincent 540IVincent is offline
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Location: San Ysidro, CA, USA
 
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Mein Auto: 1997 BMW 540I
Thanks for the link. I actually had a broken p/s side mirror which is heated with memory that I replaced today thinking that this might be affecting the temp sensor but no affect. I also reset the instrument cluster in test 21 using the onboard diagnostics in the cluster. This ended up changing the the temp from -66 (which it read all day) to -122, then I drove around for about 10 minutes and it went down to -114. Now I am not sure if it is actually reading negative or not as my pixels are screwed up on my cluster so it may actually be reading positive but I do not think so because the A/C is still blowing warm air. I am going to try jumping the two wires to see if this will calibrate it. This is really frustrating. Thank you again for the link, I will let you guys know if it works out.

Vincent
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Old 10-21-2013, 10:04 PM
L0F L0F is offline
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Location: chicago
 
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Mein Auto: 3/98 528i
Ambient Temp Reading Has Gone Nuts Unlike No Other I Have Read About

That's very strange, never heard of one of these sensors behaving like this before. I would disconnect my battery and see if it fixes itself once you reconnect it.


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  #5  
Old 10-22-2013, 01:11 PM
540IVincent 540IVincent is offline
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Location: San Ysidro, CA, USA
 
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Posts: 19
Mein Auto: 1997 BMW 540I
I will try a hard reset when I get home today. One question I have, does the temperature read out on the instrument cluster read for example + 75, specifically does a +/postive symbol show when the temperature is +/positive? I know the -/negative symbol shows when the temp is below zero but I need to know if there is a +/postive symbol that will show when the outside temp is above zero. My pixels are bad on my cluster and last night after resetting it, the reading was -122 but I do not know if it was actually showing +122 perhaps because the pixels that would show positive are burned out and the symbol ends up looking like a negative symbol when in reality it is a positive symbol. Hope this makes sense. Thanks again to all for your help.

Vincent
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Old 10-22-2013, 04:58 PM
L0F L0F is offline
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Location: chicago
 
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Mein Auto: 3/98 528i
Ambient Temp Reading Has Gone Nuts Unlike No Other I Have Read About

My cluster always shows the positive + symbol when temps are above zero, sounds like your pixels being out is throwing you off.

I just repaired my sensor, the actual plug for the sensor went bad causing -40 to be displayed. I ordered the repair kit, but also had a spare sensor lying around. I removed some material on the back of it and wrapped the prongs with wire and soldered it.

Then to test it I twisted up the wiring with harness, after ten minutes the display showed -39, it moves up to the real temp very slowly.

Being impatient, I soldered and heat shrunk everything, used some liquid electrical tape on top of that. The next day when I turned my car on everything was back to normal.


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  #7  
Old 10-24-2013, 11:20 AM
540IVincent 540IVincent is offline
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Location: San Ysidro, CA, USA
 
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Mein Auto: 1997 BMW 540I
Thank you so much for the reply. Yes, the lack of pixels has been throwing me off as my cluster is now reading the correct temp outside or close it. Today it was fluctuating between -64 and -72 but in reality I am sure it is reading +. Still my A/C is blowing warm air but since I recently purchased the car I think the A/C just needs to be recharged. Thanks again to all for your replies and help, I really appreciate it.

Vincent
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