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Unread 09-04-2012, 11:02 AM   #1
Bale
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1998 ZJ 
 
Join Date: Jul 2011
Location: Jeep Heaven, Norway
Posts: 74
Ambient temperature sensor not working

The overhead display always shows 0 degrees.
Any tips on what the problem might be? Broken signal wire? Dead sensor?

How can you troubleshoot and fix it?

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Unread 09-04-2012, 02:56 PM   #2
jaguarjoe
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On my '95, the sensing thermistor is in front of the radiator near the bottom. It goes to terminals 9 & 10 on the OH console. The wires are Dk Grn/Red (9) and Lt Grn/Wht (10).

A thermistor changes resistance with temperature. Cold = high ohms, Hot = low ohms. If you put an ohmeter across the sensor and heat and/or cool it you'll see the resistance vary. If it is 0 ohms or infinite ohms, the sensor is faulty. Thermistors come in hundreds of values, I do not know what the sensor value is supposed to be. Go to the P n P and buy one for 50 cents.

If you go to Radio Shack and buy a ~50,000 ohm potentiometer, You can feed that into the console with the sensor unplugged. Turn the pot and see the readout change. If it doesn't change, the console is faulty.

Hope this helps
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Unread 09-04-2012, 05:31 PM   #3
AVR2
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You can try doing the overhead console self-test: hold down the two buttons under the display and then turn the ignition on. Continue to hold the buttons down until all the segments in the display light up. The display module is now performing its diagnostics and will do one of three things: if everything is OK it will return to normal operation; if its internal circuitry is faulty it will display "FAIL", and if it is not receiving all the CCD messages it needs (which can include the temperature data) it will display "CCD".

The resistance for the sensor should be between 2k and 350k.
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Unread 09-04-2012, 06:59 PM   #4
jaguarjoe
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Quote:
Originally Posted by AVR2 View Post
The resistance for the sensor should be between 2k and 350k.
That means almost any or every thermistor will work. Kinda hard to believe it would especially constrained by the <12v system inside of the console.
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Unread 09-04-2012, 07:01 PM   #5
AVR2
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Quote:
Originally Posted by jaguarjoe View Post
That means almost any or every thermistor will work. Kinda hard to believe it would especially constrained by the <12v system inside of the console.
Those are the resistance figures to look for according to the factory service manual.
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Unread 09-05-2012, 12:20 AM   #6
Bale
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Thanks!
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Unread 09-05-2012, 01:21 AM   #7
moggie99
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New sensors are very cheap online - I bought one from Rockauto and the current price is just over $16.
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Unread 09-05-2012, 02:10 AM   #8
jaguarjoe
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THIS is cheap:

http://www.allelectronics.com/make-a...RMISTOR/1.html
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