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2018 Yamaha f90xb code 15

S

Shedden1003

New member
Howzit Guys,
scratching my head and trying to trouble shoot over here. Changed the thermostat on my f90 today and now my engine warning indicator light is blinking. When I hold mode on my tach to get a code I receive the code 15 which is incorrect temperature sensor signal. I double checked to make sure it was the correct thermostat part number and it is. Even when I replace old thermostat I receive the same code and the blinking warning indicator. Even swapped the thermosensor but still has blinking warning indicator. Engine starts up fine and runs good but definitley has a harder time starting when warm. Any help greatly appreciated . Thank you
 
FIXED! I own a 2018 Yamaha F90LB and changed the thermostat and had the same symptoms. In my case the water temperature read low on gage and the digital temperature indicator on my Garmin gps was 104F. That temperature is the default when the temperature circuit malfunctions. When cold it starts fine but when hot it is hard to start because of excessive fuel by default for a hot engine. I traced my issue to a broken 5 volt reference black-yellow thermosensor wire. It was probably pulled during the thermostat change. The insulation remains intact but at the break the copper wire had separated. You can measure a distinct difference in diameter as well as missing the expected 5 volt signal needed for engine temperature measurement. 0.95 mm for wire in tact and 0.500 where separated. The other wire to the sensor is black and acts as a ground for the thermosensor circuit. Yamaha only lists a new $600 harness rather than a pig tail. I was able to make a repair to the existing wire.
 
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