# P1126 MIL code = failing thermostat?



## OldAltima (Oct 13, 2016)

Hi,

I have a 2001 Altima GXE with 252,000 miles on it and still rolling.
I have a question about P1126 MIL code.

The SES light turned on after I refilled the gas with 91 octane (usually I use 87) and after 1 hour driving constantly on a long highway to Yosemite in a bit chill weather of Christmas day.
The temperature gauge wobbled up and down between 1/4 and 1/3.

SES light never turns on when I drive around city or below 75 miles distance (stop and go).
I live in San Jose California, temperature gauge usually runs normal (1/3) when I drive around city or Bay Area highways.

I read in engine-codes.com site, it's caused by failing thermostat (can't close).
Is that true P1126 MIL code is caused by a failing thermostat for 2001 Nissan Altima? 

Thank you and best regards.


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## smj999smj (Jan 1, 2006)

Most of the time, it's the thermostat. The code sets when the engine doesn't reach normal operating temperature after an appropriate amount of time. Low coolant or a bad engine coolant temp sensor can also set the code. If possible, stick with a genuine Nissan thermostat.


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## OldAltima (Oct 13, 2016)

Thanks for the information @smj999smj ! Really appreciate it.


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