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Discussion Starter #1
I took my Z out for a drive today - it had been sitting for about 3 days. Then I looked down at the temp gauge and it was pegged out at max 260 deg ... The DIC also read "Coolant Temp XXX deg F". No warning messages or lights. The car doesn't seem to be running hot (oil temp <207). Is it possible for the coolant temp sensor to go out immediately (like shutting off a light bulb) ? I checked and wiggled the wiring around the sensor a little, but couldn't tell anything out of the ordinary. Also, I notice both fans were running when I pulled it into the garage. Coolant level looks good. Car is 7 years old with 19k+ miles - never had any problems.

Coincidently, I just changed the Optima battery out for a new one today also - I don't think I disturbed anything doing this ...

Will this hurt the car to drive 200 miles to the dealer to replace under extended warranty with the high reading ? Also need to flush / replace the coolant due to time.

Any input welcome. Thanks.

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Watch the oil temps instead of water. Provided the oil stays below about 250F, there's no question that the cooling system is working and the water temp data is bogus and you can safely drive the car.

Almost certainly, the sensor is disconnected or just bad and yes, they can fail spontaneously. I'm surprised the car didn't go in to "Reduced Power", since I thought the PCM used water temp to decide, and 250-ish is the magic temperature. There must be another temp sensor someplace or maybe the DIC uses Oil temp instead of water...
 

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Discussion Starter #3 (Edited)
Thanks.

Additional info: Later, when the car was almost cooled down , I turned the key on and started the engine. The temp gauge swept up to max 260 initially per normal operation on startup, then went down to 122 deg F for about 1-2 seconds (along with the DIC reading), and then immediately went back up to max and stayed. I assume that the coolant temp was about 122 at that time. Still think it may be the sensor ?

Both engine fans kicked on also at that time.

Input welcomed. Thanks.
 

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Wow I just started having this exact same problem yesterday freaked me out for a sec, but I drive with my Oil temps on the DIC, so it was just a sec...as i saw my oil temp at a 199 deg.

Anyone else run into this, i haven't had the chance to "wiggle wires" or reset the PCM yet, did anyone resolve this replacing the water temp. sensor?

Thanks
 

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Well seems my problem was resolved. I reset the PCM, then after the guage would read normal for about five seconds it would just peg (xxx F degs) all the way out. This was giving a P0116 C DIC code. I reset that code, and the gauge began to read normally again, and has been since i did this on wednesday.

Just wanted to get this down for future searches.
 

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Well seems my problem was resolved. I reset the PCM, then after the guage would read normal for about five seconds it would just peg (xxx F degs) all the way out. This was giving a P0116 C DIC code. I reset that code, and the gauge began to read normally again, and has been since i did this on wednesday.

Just wanted to get this down for future searches.
Thanks for the feedback.

Mike
 

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If you want to know if the water temp sensor itself is bad is use a Ohm Meter across sensor's pins and ground with wiring connector off the sensor

As example if the sensor was seeing 260 degs the ohm meter should show about 77 Ohms
By rights if temp was that high the PCM would have thrown a DTC high temp

degF Ohms
302 47
284 60
266 77
248 100
230 132
212 177
194 241
176 332
158 467
140 667
122 973
113 1188
104 1459
95 1802
86 2238
77 2796
68 3520
59 4450
50 5670

Weak battery can cause odd false conditions or water temp sensor gets it's ground via the engine block.

At back of left side of engine is a flat ground wire that goes to ground, check both ends of wire connectors as clean and tight.
 

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I've got a 98 c5. My temp gauge goes to overheat shortly after start up and the fans kick on. This happens with the temp sensor plugged in or unplugged. I've replaced the sensor twice, ohm out the wires checked good and changed the ecu with the same results. The grounds all checked good also. I'm desperate, please help. Any ideas will be appreciated. Thanks in advance.....
 

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Check the Tstat being stuck mostly in closed position
How's the radiator coolant hoses, check if too soft and collapses under load

How about the water pump or belt working correctly ?

Check the flat ground wire from back of left head to frame ?
 

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I've got a 98 c5. My temp gauge goes to overheat shortly after start up and the fans kick on. This happens with the temp sensor plugged in or unplugged. I've replaced the sensor twice, ohm out the wires checked good and changed the ecu with the same results. The grounds all checked good also. I'm desperate, please help. Any ideas will be appreciated. Thanks in advance.....
Im having the same problem, do you found the problem?
 
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