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On the way to work this morning, my 2010 Canyon I4 temp gauge dropped all the way down. Showed no temp at all. Then dash pops up and says Ac off. I was hoping someone could give me an idea of anything it could be other than thermostat. I’ll be changing the thermostat in the next day or so to see. But if that doesn’t fix it, I’d like some ideas of other things to look at from others who have had this issue
 

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On the way to work this morning, my 2010 Canyon I4 temp gauge dropped all the way down. Showed no temp at all. Then dash pops up and says Ac off. I was hoping someone could give me an idea of anything it could be other than thermostat. I’ll be changing the thermostat in the next day or so to see. But if that doesn’t fix it, I’d like some ideas of other things to look at from others who have had this issue
Replacing the thermostat is a lot of work/expense to confirm that most likely it is not the cause of problem. If the thermost was stuck wide open you would still see a temperature reading of 1/4 dial or more. If the temperature indicator is not reading any temp at all, there is a problem with the sensor, the wiring or the indicator. Less likely, the ECM. If you know someone with a scan tool have them check to see what the ECM is indicating for temp. If there is a temp reading there, suspect the indicator.
 

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On the way to work this morning, my 2010 Canyon I4 temp gauge dropped all the way down. Showed no temp at all. Then dash pops up and says Ac off. I was hoping someone could give me an idea of anything it could be other than thermostat. I’ll be changing the thermostat in the next day or so to see. But if that doesn’t fix it, I’d like some ideas of other things to look at from others who have had this issue
My understanding is that upon starting, if the computer doesn't see a certain amount of temperature rise in a certain period of time, it will do just what happened to you. In most of the cases that I've heard of, the culprit is the thermostat being stuck partially or fully open (not allowing the engine temperature to rise enough quickly enough to suit the computer). If you have the ability to check your codes, you can verify this. And if there is a code, it will not go away on its own but if you reset it, it will go away until the next time the computer sees the same conditions. Driving on the interstate (or similar conditions) right after starting up will cause the code to occur more than if you are doing stop and go city driving right after starting the engine.

Edited: P0128 is the code that causes the issues that you experienced.
 

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AC off is a good indication to change the thermostat. At least changing it fixed the problem with my '09.
 

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I had the same problem. The way it presented itself, it seemed like it wouldn’t be the thermostat.

If you can access some sort of code reader, monitor the ect live data while the issue is occurring. Likely, the temperature will be rising at the time the gauge drops and the ac off message is displayed. If the temperature continues rises to normal (mid 170s for stock thermostat or mid to high 180s for a thermostat that has been replaced) after the symptoms you have, it is likely a stuck open thermostat.

It won’t pass emissions tests with the check engine light on, which will be coming soon if it hasn’t already popped up, but as long as you have a way to monitor the temperature and can live without ac, it would be ok to drive on it for a while. The code sets after the conditions happen twice within the same drive cycle.
 

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Replace the thermostat. Every time I have heard of this happening and personally experienced it, it was a bad thermostat. It may be opening up slow so computer doesn't see engine getting up to operating temperature within the time limits and thinks faulty sensor and errors on the side of caution and drops gauge down and kills AC. If it has electric fans, they go to high automatically to try and keep engine cool.
 

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I recently had this same issue with my 08 with the I5. I was so sure it was the temp sensor because the temp gauge would intermittently drop out to 0 instead of just running cooler than normal. Also I had at least one cold start that showed the AC OFF warning which I thought meant the sensor was not working so I replaced it. Didn't fix the problem though. So I replaced the thermostat and it has been fine ever since. Good luck!
 
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