Post Engine Swap - P0118: Engine Coolant Temperature Circuit High Input

Just finished doing an engine replacement. I ran it for 20 minutes or so and ran it up and down the road a half dozen times.
Engine runs well when cold but very rough when warm which makes sense considering the following errors.
Water pump runs continuously.
Does not appear to be overheating or have not blown that gasket yet.
P0118: Engine Coolant Temperature Circuit High Input
P3191: Unknown code
I tested the sensor, continuity appears to be in spec, I think but I'm no expert.
And I have 5 volts at the sensor wire which I think is correct.
When the sensor is unplugged completely Water Temp Dummy Light on Dash Illuminates.
When the sensor is plugged in,the light is not illuminated - this makes me think something in the car can 'see' the sensor.
Where do I go from here??
Do I need a 'Tech Tool' better than a OBDII Scanner tool to reset the code?
I have checked the thermostat,it's ok.
Thanks so much !
Chris