DTC P2251-00: O2 Sensor Reference Ground Circuit/Open (Bank 1 Sensor 1): General Description

The normal operating temperature of the Heated Oxygen Sensor (HO2S) ranges from 350 to 850°C (662 to 1562°F). HO2S heater greatly decreases the amount of time required for fuel control to become active. The ECM provides a pulse width modulated control signal to adjust current through the heater. When HO2S is cold, the value of the resistance is low and the current in the circuit is high. On the contrary, if the temperature in the resistor of the HO2S rises, the current drops gradually.