Ambient air temperature sensor high voltage

[Ross Bezvy]

Hi.
I have a 2009 ProStar Premium with Cummins ISX
I've got a yellow triangle on my screen and when I've made a diastolic it said me next fault:"Ambient air temperature sensor 1 circuit-voltage above normal or shorted to high source.High signal detected at ambient air temperature circuit."
I went to 3 dealers.And all of them keep telling me different sensors I need to change.
On the last dealer we checked under the radiator,inside of the driver mirror and by the fifth wheel and didn't find any sensor.But on the diagram it shows that I need to change some other sensor by the ECM.
Could someone help me please.
In the end I don't even know what I am looking for and where it should be.
Thank you a lot.