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I have noticed a few times that the temp reading is sometimes not accurate. It has been off 10 to 30 degrees and fluctuating. Once recently it read 15 degrees and gave that "possible ice on road" warning. Maybe it was being wishful as temps here have been in the high 90's with heat index over 100. Has anyone else noticed this? are there possible side effects of the outside temp being incorrect?
 

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Dont forget the temperature sensor is on the drivers side mirror which is black plastic so the sun will increase the reading. It hangs down under the mirror as a little nub. High readings on days the sun is hitting that mirror sitting still would not surprise me. That doesn't explain the low reading and Ice warning at 90º. Defective or wire connection? I just had that mirror changed out so I better check mine!
 

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outside temperature sensor error

You are going to luv this. My outside temp reading on Promaster varies from 165F to 35F while driving in 77F weather. Obviously the sensor has failed. It is located in the bottom of the drivers side mirror. Went to Chrysler to get a new one. Not available, have to buy the whole mirror for $390. Went to every auto parts store in town and no luck, complete mirror only. I removed the sensor and found manufact online, made in Italy, can't order it. That is the bad news. The good news is there are 2 simple solutions. The sensor is a 2 wire thermistor rated at 10,000 ohms at about 77F. So if you go to Radio Shack or Amazon and buy a 10K resistor (1/4 or 1/8 watt rating) and just remove the old sensor and solder it in you will have a reading of 77F all the time, winter or summer. This is great for peeps that dont like real hot or real cold weather because its always 77F no matter the season. But it eliminates the check engine light problem from the failed sensor. Solution #2 is to replace it with an outside temp sensor for any 2015-2018 Dodge Ram 2500 pickup which is available at any parts store. I bought one from Amazon (chrysler # 5149265AB) for $18. Just cut out the old one and solder in the new one. You will have to cut some useless plastic fins off the new one to solder wires directly to it since it really is supposed to mate with a plug. Easy fix with a small set of diagonal pliers. Just don't harm the sensor or elect pins that you are soldering to. Also i had to drill a new 1/4" hole in the bottom of the plastic mirror housing so that the new sensor would not interfere with the internal mirror parts (it is slightly bigger than the original). The new one reads exactly correct against an expensive hand thermometer that i have. Sounds complicated but it really is a simple changeout. Also i used some Goop glue to hold the new one in place. Now it happily sticks below the mirror like the original. Also be advised that you can order replacement mirror glass from Amazon and just glue it over the old broken mirrors if you have to. Mirror motors and heaters still operate nicely. Hope this helps someone.
 

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Hi,
10K thermistors are very common -- they can be had on Amazon for not much more than a dime a dozen.


[ame]https://www.amazon.com/Uxcell-a14092200ux0209-Thermistors-Resistor-MF52-103/dp/B0166I8IU8/ref=sr_1_3?keywords=10K+thermistor&qid=1557336678&s=gateway&sr=8-3[/ame]


Amazon also has them enclosed in a little stainless can, which might be a good choice? Also cheap.


Since they are just resistors that change resistance with temperature, you can't hook them up wrong -- reversing the leads makes no difference.


My temperature readings are also eratic at times, and then go back to normal.


Gary
 

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I confirm the problem of having to replace the whole mirror. I was able to do it just 15 days before the warranty expired. They told me the only way was to replace the whole mirror, over $ 500 here in Canada.
I'm sure one can tweak the thing by replacing the thermistor and installing it somewhere outside. The connector is inside the driver's door.
 

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I have similar issue with engine light is on with P0073 related to ambient temperature sensor. I follow instruction on here and youtube, and got the mirror housing cover off. Found the sensor wire was pinch by the housing cover and somewhat shorted the sensor. So i just cut the bad wire out and resolder it and test the sensor is good and put everything back. The sensor was working great until the next morning and the temp read on the dash is off again. No engine light as of yet but my OBD reader is showing pending P0073 code. I might need to get one of the above sensor and re-solder it again.

I been thinking I should relocate it to another location so if the sensor goes bad, it can be easily replace. But haven't figure out how to rewire without a wiring diagram.

Does anyone know why the ECM need ambient temp input? It just dumb that it will trigger engine light when its not related to the engine control. Some said its used by the A/C but mine is blowing cold.
 

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Does anyone know why the ECM need ambient temp input? It just dumb that it will trigger engine light when its not related to the engine control. Some said its used by the A/C but mine is blowing cold.

I think that the ambient temperature is used in cold weather. I have read that the motor won't start when it's too cold (-30C/-22F or so) and the idle runs higher below freezing temperatures (1,100 RPM instead of 800 RPM).
 

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For some reason I'm thinking engine management uses that temp reading for air/fuel ratio . Which is emission related , different warranty .
Seems unlikely critical engine function would be monitored by a sensor mounted on a vulnerable mirror. If there is an engine air temp sensor, wouldn't it be inside the air intake duct/manifold where it counts?
EDIT: phil beat me to it
 

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No... The outside temp probe on the mirror has nothing to do with emissions...

IAT is an acronym for Intake Air Temperature. The IAT sensor measures the air temperature that is going into your intake manifold. The colder the air, the more dense it is, and the more fuel you need to keep your engine happy. Coool ....literally. Almost all IAT's are simple two wire devices that measure resistance. As the air temperature changes, the resistance in the sensor changes and the ECU knows to change the A/F ratio based on this. Combine this data with that of the MAP sensor and your computer can now give a pretty accurate guess of the volume of air moving through your engine. This is great news, but it's all based on calculations, instead of real solid numbers. This is where speed density is tossed aside and big Mr. MAF enters the party

Usually the IAT is tied in with the MAP on the promaster.

If the outside air temp on the mirror controlled the emissions computer you'd be having a lot more problems ....
 

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So, I finally fixed my ambient temperature sensor.

The most difficult part is to remove the door panel, but it is not that hard if one follows these guide lines:


As the picture shows, the gray connector (with the brownish wires) is the one that leads to the faulty temperature sensor in the mirror. I bypassed it and simply connected a 10K NTC thermistor ($2 @ amazon).

Of course, the temperature indicator won't reflect the exact outside temperature, but I don't care, just glad I got rid of that "Check engine" warning light.
62121


Cheers!
 

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Same thing happen to me on my 2016 MH as the temp sensor showed 134*F with the outside temp of 55*F. The temp sensor controls the A/C output and the whole mirror has to be replaced. Replaced under warranty. This is a know problem that they know about. Other owners have done their own replacements as stated in other posts. Bad Outside Air Temp gauge.jpg
 
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