Codes P0128 and P0000, where is the coolant temperature sensor located?

2018 TOYOTA HIGHLANDER
45,000 MILES • 3.5L • 6 CYL • 4WD • AUTOMATIC
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MAS77RO
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Hi there. I would appreciate your take on this one. Check engine with a P0128 came on - the car did not warm up the way it should, the idling was a bit higher than usual, temperature indicator stayed low on highway drives - other than that it ran fine. The dealership suggested the thermostat needs to be changed. Did that.
The next day, on a cold morning, I noticed that the car did not warm up again the way it should. When scanned, the ODB tool alternates between a P0128 and a P0000 code - all this without a check engine light. Thank you
Jan 19, 2022 at 1:05 PM
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JACOBANDNICKOLAS
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Hi,

First, the P0000 is really an odd one to see. It basically means nothing or there are no codes. The P0128 simply indicated the engine isn't warming up in an acceptable amount of time. Often times this is a stuck open thermostat, but it can also be related to the engine coolant temperature sensor not working properly. Remember, if the PCM receives a signal from the sensor, it doesn't know if it is right or wrong. Instead, it knows there is a signal and that is what it goes with.

What I would suggest at this point would be to inspect the engine coolant temp sensor. If you look at the pics below, they provide the directions for testing.

Try this and let me know what you find,

Joe

See pics below.
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Jan 19, 2022 at 7:21 PM
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MAS77RO
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Hi Joe,

Thank you for your reply. Where is the sensor located?

Jan 19, 2022 at 8:13 PM
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JACOBANDNICKOLAS
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Hi,

If you look below, it shows sensor location. To test it, it will need to be removed. Pics 2 and 3 are the vague (LOL) removal and replacement directions from my manual. Here is a link you may actually find more helpful.

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Let me know if this helps or if you have other questions. Also, make sure the connector isn't loose, damaged, or corroded inside when you check.

Take care,

Joe

See pics below.
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Jan 20, 2022 at 5:49 PM
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MAS77RO
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Much appreciated. Thank you, Joe
Jan 20, 2022 at 5:53 PM
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JACOBANDNICKOLAS
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You are very welcome. Let me know how things turn out for you, and if I can help in any way.

Take care,

Joe
Jan 20, 2022 at 7:28 PM