The correct function of the engine depends largely on the stoichiometric air/fuel ratio: 14.7.1. To achieve this, the ECM (Engine Control Module) depends on the readings of the Oxygen Sensors (HO2S), which notices the oxygen content in the exhaust.
The information regarding the oxygen content in the exhaust is sent to the ECM. Then, the vehicle computer adjusts the fuel that goes to the engine. The Oxygen Sensors have a circuit that operates a heating device, which is responsible for increasing the temperature of the sensor, thereby shortening the time needed by the engine to achieve a closed cycle, reducing emissions.
If the ECM finds a fail in the heater circuit of Oxygen Sensor Number 1 in bank 2, the error code P0050 OBDII is set and the Check Engine light is illuminated.