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Unread 06-30-2011, 01:02 PM   #1
Codioos
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1997 TJ Wrangler 
 
Join Date: Jun 2011
Location: Spokane, WA
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TJ False engine Temp

Hi all,
I'm a new member but have been using your site for a year now to resolve issues with my TJ. However there is one issue I cant seem to find a solution to. I have a 97 TJ with a 4.0L and the engine temp gauge always reads about 235-240. I replaced the t-stat and no change. I then replaced my temperature sensor, also no change in temp. I used a computer to plug into the wiring and found out my Jeep is running at normal temperatures (198-212) and also confirmed the temperature with a hand-held temperature sensor that I used on the t-stat housing and it also gave me a reading of 205-212. So it appears its my temperature gauge...? Any other ideas of why I have a false temperature gauge reading or am I missing something? Also, has anyone ever had this problem and any ideas of fixing it? Its just nerve racking to see your temp near the red line, even when you know its not. Thanks in advance!
-Codioos

P.S. When I start it up in the morning the temp immediately reads about 130. Thanks!

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Unread 06-30-2011, 01:12 PM   #2
DevilDogDoc
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Location: Yucca Valley 20 miles from Johnson Valley, CA
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The sensor on the housing feeds the PCM, the one on the block by the firewall feeds the gauge I do believe. Might look at that one.
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Unread 06-30-2011, 01:34 PM   #3
Codioos
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Quote:
Originally Posted by DevilDogDoc View Post
The sensor on the housing feeds the PCM, the one on the block by the firewall feeds the gauge I do believe. Might look at that one.
Thanks for the fast reply! I cant seem to locate another sensor near the firewall, although I have heard of there being another sensor other than the one on the t-stat housing. Is it on the driver/passenger side? Under the manifolds? Thanks!
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Unread 06-30-2011, 01:43 PM   #4
DevilDogDoc
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Back of head on drivers side. One wire going to it.
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Unread 06-30-2011, 02:20 PM   #5
LJameson
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Quote:
Originally Posted by DevilDogDoc View Post
Back of head on drivers side. One wire going to it.
TJ's don't have the coolant temperature switch like earlier 4.0s. The gauge goes off of what the PCM reads.

Since your scan tool is saying the PCM reads the correct temperature, I'm gonna say it's the gauge. Try holding the odometer reset while you turn the key to the on position (but don't start the engine). It will go through a sequence with all the gauges and youll know it's off when the gauge goes past 260.
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Unread 06-30-2011, 02:58 PM   #6
Codioos
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Quote:
Originally Posted by LJameson View Post
TJ's don't have the coolant temperature switch like earlier 4.0s. The gauge goes off of what the PCM reads.

Since your scan tool is saying the PCM reads the correct temperature, I'm gonna say it's the gauge. Try holding the odometer reset while you turn the key to the on position (but don't start the engine). It will go through a sequence with all the gauges and youll know it's off when the gauge goes past 260.
I cycled the gauges and they all seem to work okay, and yes the temp gauge goes past 260, but most of the other gauges go past red-line too. No such luck with the temp sensor on the block near the firewall. I have heard that if you disconnect both the battery cables and then hold them together for a few seconds this will reset the computer.... Is this safe? and will it possibly rest the temp gauge?
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Unread 06-30-2011, 03:03 PM   #7
Dabbill
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Touching them together just discharges the system quicker, if you dont want to hold them together, just leave them unhooked over night.
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Unread 06-30-2011, 03:57 PM   #8
Jason
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Originally Posted by Codioos View Post
P.S. When I start it up in the morning the temp immediately reads about 130. Thanks!
So this part got me thinking... Is it possible the needle for the gauge has been removed an re-installed in the wrong spot? Sometimes the needles need to be removed for those fancy white or reverse illumination overlays.
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Unread 06-30-2011, 04:14 PM   #9
Codioos
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Originally Posted by Jason44406 View Post
So this part got me thinking... Is it possible the needle for the gauge has been removed an re-installed in the wrong spot? Sometimes the needles need to be removed for those fancy white or reverse illumination overlays.
Well when the key is off and out of the ignition, the gauge falls below 100 but then when you turn the key to "on" the temp immediately reads ~130 when the engine is cold. Its like the gauge (or something..computer?) thinks its constantly at 130 when the engine is cold. I don't think this jeep has been messed with as far as the needles or aftermarket overlays go because it wouldn't fall below 100 when you turn it off.
Also, after I held the odometer button and turned to "on" to cycle the gauges, the temp goes all the way past 260 and then back down below 100, then once the cycle is complete it goes back to 130....
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Unread 06-30-2011, 05:37 PM   #10
Codioos
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So I called my local Jeep dealer and talked with service. After explaining my situation with the them I was told that its not likely to be the PCM being that when I hooked up the scan tool I was given an accurate temperature reading. He told me it was most likely the gauge or a worn wire. So I tore my dash apart and took out the cluster. Behind the cluster I found a wire that had been directly wired into one of the main connectors to the back of the cluster and the wire ran to another wire located on the main wiring harness connecting to the steering column.... WTF. The wire that is tapped into for the gauge cluster is Red with a grey stripe and it is wired into the main steering column wiring harness to a solid Red wire. Any ideas what those wires are, and why they have been connected to each other??
Also, this Jeep at one time had an alarm hooked up. As far as I know this alarm was taken out and just the little indicator lights remain, which are not plugged into anything. Sigh... hope I didn't just buy an electrical nightmare.
A little more information on my rig: I have also noticed that I cannot have both my driving lights and fog lights working at the same time. Meaning that when I have them both connected there is a relay behind the glove box that starts making all sorts of noise, if I unplug the relay then the noise stops (duh) and then I lose my fog lights but the driving lights are okay. There are two relays behind the glove box that look the exact same and are hooked to each other...its the one on the left that makes the noise. What a can of worms.
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Unread 06-30-2011, 05:45 PM   #11
Codioos
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Instrument gauge harness


Steering column harness
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Unread 06-30-2011, 09:47 PM   #12
Codioos
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Quote:
Originally Posted by Jason44406 View Post
So this part got me thinking... Is it possible the needle for the gauge has been removed an re-installed in the wrong spot? Sometimes the needles need to be removed for those fancy white or reverse illumination overlays.
Holy cow. You were right. I decided to take the needle off the gauge and reinstall it, and now it works perfectly. Way to go Jason!
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Unread 07-01-2011, 07:22 AM   #13
Jason
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Originally Posted by Codioos View Post
Holy cow. You were right. I decided to take the needle off the gauge and reinstall it, and now it works perfectly. Way to go Jason!
Cool. Sometimes the simplest answer is best.
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