Outside Ambient Temperature Sensor Explained - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 10 (permalink) Old 08-08-2011, 12:42 PM Thread Starter
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Outside Ambient Temperature Sensor Explained

I was having trouble with my outside temperature readings being off, finally fixed mine by cleaning the connector on the sensor.
In the process of looking for the fix I gathered information from many places on the internet. Below is a summary - the technical good stuff was posted by a Jeep tech in the UK.

First the location of the sensor - just behind the right most section of the grill - see pictures attached. To remove it you can reach under the front fender and grab the assembly - twist and pull it slightly to the rear and it will come loose. It will now hang down below the fender. Remove the sensor from the wires by holding down the small tab and pull the sensor away from the wires. When reinstalling be sure to use the right side tab not the one behind the second grill opening - don't ask how I know

The sensor is a Thermistor - opposite of a resistor - the hotter it gets the less resistance it has.

DIAGNOSIS AND TESTING - AMBIENT TEMPERATURE SENSOR
Part Number 56042395
Turn the ignition switch to the Off position.
Disconnect the ambient temperature sensor wire harness connector.
Measure the resistance of the ambient temperature sensor. At –40 C (–40 F), the sensor resistance is 336.6 K ohms. At 60 C (140 F), the sensor resistance is 2.49 K ohms. The sensor resistance should read between these two values. If not OK, replace the faulty ambient temperature sensor. (at about 78 degrees F mine read 8.5K ohms)
If the resistance seems OK, make sure the connector contacts on sensor and loom are clean and have no corrosion. With the sensor unplugged turn on the ignition, the temp should read OC. Short the connector where the sensor would be and check the temp it should read SC

How the CNN (computer circuit/ display) works
Vehicle with the key off for more than 4 hours...The CCN will
update the ambient temperature reading immediately.

Vehicle with key off for more than 2 hours but less than 4
hours....The CCN will update the ambient temperature reading
immediately after vehicle reaches above 20 mph (with no duration
constraint) and will update every 500 ms (1/2 second) thereafter.

Vehicle with the key off for less than 2 hours...The CCN will
display the last temperature reading (which is stored in memory)
just prior to the ignition being turned off. The CCN will not
update the value in the display until the car has been driven at
20 MPH or above for 3 consecutive minutes. If the vehicles
speed and drive time does not meet the criteria the CCN will
continue to display the stored value until the criteria is met.
Once the criteria is met, then the CCN will update the display
every 500 ms based off of the ambient temperature sensor output.

(This confuses most of us when driving on short trips)
They probably want some air flowing past the sensor after sitting in front of a hot engine to get the correct temperature before showing the temperature on the display.
Bottom line don't worry about the temperature accuracy until you have gone 20MPH + for at least 3 consectuive minutes.
My 05 Grand Cherokee updates all the time - just this mess on my 06 Commander.
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06 Commander Limited Hemi - QDII,
Past -89 Comanche, 98 Grand Cherokee (2WD), 2000 Cherokee, 05 Grand Cherokee Limited 4.7
Had to replace the brakes - they opened more gas stations in town
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Last edited by rblapham; 08-10-2011 at 02:56 PM.
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post #2 of 10 (permalink) Old 08-08-2011, 02:33 PM
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Good info. I always wondered where that damn sensor was.
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post #3 of 10 (permalink) Old 08-08-2011, 05:33 PM
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That makes sense now. Example: In the Quilcene wildlife wilderness, we made frequent photo stops. We were also in low range for over 100 miles before ever coming back out to civilization. The temp was stuck forever at 79 degrees, which became BS after a while. (It was hotter than the hubs of heck later in the day) There were hours of never getting even close to 20 MPH.

After a camp, it was reading lower the next day, but pulled the same crap. Later, it was reading reality, and I thought it was just going intermittent. Now, I know we were on the highway when it started reading again.

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post #4 of 10 (permalink) Old 08-09-2011, 12:12 AM
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More good info! I learned some of this the other day too, but was under the impression the EVIC self diagnosis would display "-40" if the circuit was open and "130" if it was shorted. Is there a difference between models and years?

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post #5 of 10 (permalink) Old 08-09-2011, 07:50 AM Thread Starter
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Yes showing -40 or +140 was another option instead of the OC or SC. Do not know what vehicles display what. That write up was from the UK so it may be the european version. This sensor system is used in almost all Chrysler products. I didn't do the test of it unplugged or shorted - just took a resistance reading so don't even know what the 06 commander shows

By the way the sensor # 56042395 is also used in most Chrysler products. Searching for a replacement I saw prices from about $10 to $60. Think dealers charge about $25- $30 (US)

06 Commander Limited Hemi - QDII,
Past -89 Comanche, 98 Grand Cherokee (2WD), 2000 Cherokee, 05 Grand Cherokee Limited 4.7
Had to replace the brakes - they opened more gas stations in town
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post #6 of 10 (permalink) Old 08-10-2011, 07:07 AM Thread Starter
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I was thinking about this last night - boy what a confusion maker this software is. I serviced computer systems, hardware and software for over 40 years. This temperature display can be really tough to troubleshoot. Say you get up in the morning and go to check the temperature - car off over 4 hours - turn on the key and see temp - turn off and play with the sensor - turn key on again and no change. OOPS you are now in the less than 2 hour program - need to drive 20+ MPH for 3 straight minutes!! I wonder if any of the jeep service guys know about this?? That software must have been written by Murphy If the serviceman used the computer monitor, the temp will change - just not the display for the driver.
Best tip - if you try to check out the sensor - when you turn on the key after 4 hours off - leave it on and then play with the sensor. The sensor is just a thermistor (reverse resistor) and it will not hurt to play with it live.

06 Commander Limited Hemi - QDII,
Past -89 Comanche, 98 Grand Cherokee (2WD), 2000 Cherokee, 05 Grand Cherokee Limited 4.7
Had to replace the brakes - they opened more gas stations in town
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post #7 of 10 (permalink) Old 08-10-2011, 11:32 AM
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I just had an idea!

When I was playing around with the Superchips programmer, I discovered you can set it up in live data mode. (It's amazing what comes out of the diag port, and you can monitor four things at once) Seems I remember temp data. I'll have to get the thing hooked back up, and see if outside temp data is there. And, is it a live streaming data?

It just might be the updates delays are only what's shown to the driver. I have a feeling the Superchips in live data mode will be in real time. (Of course, I could be wrong. I was wrong once before, sometime in 1973 I think. )

2006, 4.7L, QTII, Toyo M/T 265/70R17 tires, Ultrasport 175 wheels, Rocky Road 2.25'' lift kit, HID off-road lighting, Surco 50x60 roof rack, Foxwing awning.


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post #8 of 10 (permalink) Old 06-18-2014, 02:03 PM
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Its really great posts.


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My '06 just started having the engine light come on with a code of P0073 pointing at the Ambient Temp Sensor, so I changed it out (it was only $19 so why not) and cleared the check engine light with my scanner. It stayed off for a bit but after about 30 miles it came back on again. and now its intermitent, the check engine light will come on here and there and then off again. Of corse this happens when my inspection is due and here in NY if you have a check engine light on for any reason your car fails
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Think about it, what part of a vehicle is the same temperature as the ambient temperatures all the time? The exterior surfaces and interior surfaces bake in the sun and get much hotter than the air, while driving the interior temps will change with AC and heat. The underside is too close to the ground and we all know how hot asphalt can get in the sun. The engine and exhaust is going to be much hotter than ambient as well, so anywhere near that is going to be way off ambient temps.

The only way to get an accurate air temp reading is to get out of the car and step 10' away from it and use a thermometer. I suppose you can tow a trailer with a tent taller than the vehicle to mount a sensor in an environment that it can give you a half accurate temp in real time.

The set up is the best they can do, its in the shade in an area that with 20mph of speed or better it can cool/heat the sensor to the ambient temp within a few minutes.

If you're driving less than 20mph in extreme heat or cold, I've got news for you, no where on your car is the temp the same as the ambient air temp, so if you need to know that, you're going to have to get out of the vehicle and step 10' away and use your own thermometer.


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