I have a 99 Neon with P1491 trouble code that shows up every morning as soon as I start the car. The code doesn't show up after resetting until a cold start. My fan comes on when its supposed to and the wiring from the fan to the relay look good. Could it be the coolant sensor or could it still be the relay?

 

Could be a faulty relay. You can swap it out with the horn relay to test it out.