New sensor was fitted (see post #15) but could it be how the ecu reads the incoming signal from the sensor/puts out the reading to the display? Just thinking out loud
Please confirm. I think you only have 1 temperature sensor and no switch? If this is the case the sensor tells the ecu , then ecu talks to dash and the fan relay trigger. ECU knows the temperature. You’ve swapped out the relay. I think you have an issue with the relay trigger , probably the crimp in relay base.