What is the PO113 OBD code on a 2003 Nissan Altima?

a P0113 is a standard protocol code. It is mandated by the EPA that the definition of the code must be the same for a Nissan, as it is a Ford, as it is a GM, a Toyoyta, etc... P0113 means IAT temp circuit #1 high input. Check te IAT(Intake Air Temp) sensor and wiring. First make sure the sensor isn't just unplugged. If somebody changed the air filter, they might have left it unplugged.