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Discussion Starter · #1 ·
My ambient temperature readout suddenly went from acting normal to being stuck at 121F last week. I removed the sensor and cleaned the contacts last night, but it didn't fix anything. There is no visible damage to the sensor. I might have had some mouse damage under the front splash piece that the sensor mounts to as the car was parked outside for a full Northern California winter, so I'm curious if anyone knows if the 121F reading is indicative of an open circuit or a shorted circuit to the sensor. Can anyone help?

I guess I should pull the panel and look for wiring damage before I go replacing the sensor.
 

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Wire harness check

BMW made a harness repair kit for the temp sensor to repair damage resulting to the existing connector/harness
assembly when it gets demolished from an incursion with a parking curb or other immovable object. To install the
repair harness, you cut away any damaged wiring and then, using the supplied splice connectors, connect the
new harness.

If one of these harness kits has been used on your car, the source of your problem is likely due to poor connections
at the splice resulting from improper crimping . Cut out the entire spliced area, then reinstall with new splice
connectors, or better yet, solder them.

It may well be the sensor itself, but I would first check the condition of wiring.

Regards,
Alan
 

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Discussion Starter · #3 ·
Good idea. I saw the splices last night when I was unplugging and replugging the connector. I'll try giving them a crimp with my crimping tool tonight and see if it wakes up again. Last night, I saw one normal reading, then it was back at 121F again this morning, which sounds like a bad connection.
 

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Good idea. I saw the splices last night when I was unplugging and replugging the connector. I'll try giving
them a crimp with my crimping tool tonight and see if it wakes up again. Last night, I saw one normal
reading, then it was back at 121F again this morning, which sounds like a bad connection.
You might want to try just clipping out the splices, strip the wires and twist them together for a quick test. Poorly
crimped splice connectors with extended time in that type of environment develop so much oxidation that the
only remedy is complete removal and and starting with fresh wire, for a more conclusive test.

Regards,
Alan
 

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I seem to recall that -40 is the value you see with an 'open'...
 

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Discussion Starter · #6 ·
Thanks, everyone.

Crimping more didn't solve anything. I need to get the undertray piece off and see if rodents have caused a short somewhere, plus I'll get rid of the crimp connectors and use solder and heatshrink tubing.
 

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Discussion Starter · #7 ·
Last night I cut the sensor wires, removed the crimp connectors and did a proper solder and heat shrink connection. With the sensor off, I verified that the reading is -40. With the sensor connected, it is usually +121, but occasionally reads normal ambient temp. Previously, I had tried unplugging the sensor and shorting the connector pins as a calibration step and it read 121, so I think that's the zero resistance value.
I think the sensor is bad (internal short), so I'm going to get a replacement.
 

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While visiting my parents this weekend I cracked the passenger side lower engine cover entering their driveway and knocked the ambient temp sensor loose. Before I noticed it making contact with the road it was damaged and is now "open" as it's reading -40 deg. My question is, if I do not replace it immediately, will it affect the engine's operation? Or is it not considered an input for the DME?
 

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Not an input to the DME, but it is an input to A/C compressor control logic.
 

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Thanks. So it does affect the operation of the climate control?
 

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Not really, I suppose. It just prevents operation of the A/C compressor so no cold air so in that regard, I guess it does.

Sent from my Motorola_i1 using Tapatalk
 

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Wow so until I fix it I won't be able to get the compressor to turn on? Guess I can't afford to put it off then.
 

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It is designed to minimize the chance of evpaorator icing in freezing temperatures. If you want or need A/C then yes, you should replace it sooner rather than later.
 
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