McRicer

I have a 2000 integra gs-r thats almost entirely stock. Literally a K&N cone filter and header. I have driven the car for over a year without this issue occurring. Now im having P0171 - System too lean code come on everytime i start the car after it warms up. Freeze frame shows that every single time the code shows up its because the coolant temp sensor tells the ECU the engine is at -40 degrees. I assume -40 means low voltage on older hondas. I have tested continuity between the sensor and ecu while wiggling the wire at both ends which showed good. I even checked the coolant temp sensors resistance which was good. I then threw a new sensor on anyway which didnt fix it. it has no other problems besides this which leaves me scratching my head. Is this a sign of a weak electrical system I.E bad battery or failing ELD? the alternator is brand new.