Ambient Air Temperature Sensor

[540i]

I have a 1993 540i -- I call her Eleanor because she's tempremental and likes to give me some shit every now and again!

Here's my question:

Every now and again (More times than not), I turn the ignition to the "Run" position and the buzzer gives me a nice "Bling". As I look over to the Ambient Air Temperature Measurement, it says -30 degrees Celcius. It is a Euro Spec BMW.

After driving for awhile (About 20 Minutes), it does it again and re-highlights the Ambient Air Temperature of -30 Celcius. I'm guessing that it re-samples the A-Temp every 20 minutes or so? Is there a known defect in the wiring harness that causes these bogus readings? Does it affect engine performance when the A-Temp reports -30 Celcius to the ECM? I would guess that it does, though I can't be sure. All of the wiring diagrams are in German and I lack the ability to read or otherwise understand much of what it says.

Any and all information is appreciated

Greg

[325isBaby]

Sounds to me as though the Ambiant Air Temp Sensor has died...when the signal goes away the DME assumes a "fail safe" programed value...at the coldest reading it will affect how much fuel is being dumped into the cyliders and what kind of timing you are running. Hopefully you find this information helpful.

[BeelZibub]

Don't know about elsewhere but a lot of euro cars bling when the outside temp drops below 3C as a hazard warning (frost and shit) my last one flashed the ambient temp at you constantly and made a bling every now and again just to keep you aware of impending doom if you didn't heed it's warning, not sure about the beamers though, I will read the manual tonight. Sounds like the sensors buggered whatever.

[BeelZibub]

Originally posted by 325isBaby@Oct 7 2004, 05:03 AM
Sounds to me as though the Ambiant Air Temp Sensor has died...when the signal goes away the DME assumes a "fail safe" programed value...at the coldest reading it will affect how much fuel is being dumped into the cyliders and what kind of timing you are running.* Hopefully you find this information helpful.

[snapback]206597[/snapback]

I guess you learned all that technical shit on your 3 year diploma eh? - but they forgot to mention the "ICE WARNING" system to you!!!

Here's a couple of quotes from around the world

On the e60 "And the ice warning sound is the most soothing I’ve ever heard"

On the BMW mini "What's that beep that seems to occur when I start the car/when it's cold?

This is not (at the time of writing) documented by MINI, but at 3° Celsius, or 37° Fahrenheit the MINI will 'beep' or 'chime' to warn of the danger of possible 'black ice' on the roads.

The temperature read out will also flash to alert you of the possible hazard."

On the E46 "When function is “active”, and if ambient temperature drops below 370F, the acoustic ice warning sounds and the ambient temperature display flashes for a few seconds. Then the display returns to the previous status. When function is “not active”, and if ambient temperature drops below 370F, the acoustic ice
warning sounds and the ambient temperature is permanently displayed."

So you spout all this crap about fuel mixtures and timing and DME just to try and make youself sound good and ascertain your value as a "TECHNICIAN", when in fact the most likely answer is very simple and has come from me - an old time "part swapper" who "gave up when the 7 series became mainstream".

LOL go talk shit to yourself.


540i I would seriuosly consider just replacing the temp sensor (found behind the front bumper on a lot of cars but not sure about the bmw) and wouldn't worry about "how much fuel is being dumped into the cyliders and what kind of timing you are running", the car is just trying to warn you (wrongly) that there's a chance of hitting ice.

[540i]

Beelzibub,

Thanks for your help. I kinda figured that it was a warning system for ice / black ice, but it's annoying to hear when it's 55+ degrees outside and it displays -30 on the display. The car runs great. Every now and again it acts up and starts dumping a lot of fuel and hunting and surging. I didn't know if the engine dumping extra fuel every now and again was directly related to the Ambient Air Temperature sending a bogus reading to the computer.

I appreciate your help on the location as well. I can only get chiltons manuals in German over here. I've looked online for them, but I can't seem to find a Chiltons manual for a 540i. I found a sender online for the 525i, and it appears to have the same pin out / functions as mine. It's $30 dollars. Does that sound about right for this type of part?

Thanks again for the awesome information.

540i

[BeelZibub]

Originally posted by 540i@Oct 8 2004, 04:44 PM
Beelzibub,

Thanks for your help. I kinda figured that it was a warning system for ice / black ice, but it's annoying to hear when it's 55+ degrees outside and it displays -30 on the display. The car runs great. Every now and again it acts up and starts dumping a lot of fuel and hunting and surging. I didn't know if the engine dumping extra fuel every now and again was directly related to the Ambient Air Temperature sending a bogus reading to the computer.

I appreciate your help on the location as well. I can only get chiltons manuals in German over here. I've looked online for them, but I can't seem to find a Chiltons manual for a 540i. I found a sender online for the 525i, and it appears to have the same pin out / functions as mine. It's $30 dollars. Does that sound about right for this type of part?

Thanks again for the awesome information.

540i

[snapback]207548[/snapback]

I don't know about prices over there but thats maybe about £20 my money - it's a lot for such a small part but hey unfortunately bmw's are a costly exercise. Hope that solves the problem, if not let us know and we'll have another bash. As far as the engine thing is concerned I would have thought the problem would be constant if the car was throwing fuel at it (as the temp it's reading is constant -31). Mines just the same at the minute and I know it's cos my MAF isn't functioning correctly (oil from an induction kit) but I can't afford to replace it yet. Try getting your hands on a fault code reader and see what that tells you.

[Torque]

My US spec makes the 'ding' sound whenever the temp gets below 38 degrees fahrenheit... which is about 3 celsius. It's just a warning thing and there is no way to turn it off.

[540i]

BeelziBub, Are you in Europe? I'm stationed in Germany. I buy most of my parts online because it's quicker than going through part vendors in Germany. I'll change it and see if that solves the problem. Thanks again!!

540i

[BeelZibub]

England mate.