I have a 2003 Ford F150 5.4...this is the first time my "Check Engine" light has came on. My temperature light has came on also, however it does not stay on which is weird to me. The ONLY time it comes on is when I am driving over 60mph, but as soon as I slow down to under 60mph it goes off and stays off unless I speed back up. Computer reads and shows code "P1299 Society of automotive engine over temp" but it is not running hot although the truck says that it is. I have checked the coolant level and it's good...I have raised hood immediately after it was on and the engine was not hot. Could it be that I need to replace thermostat if not I'm lost on other solutions and I'm looking for helpful thoughts.

Mike

 

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