OBD-II Code P0030 is defined as a HO2S Heater Control Circuit
The purpose of the oxygen sensor is to measure the oxygen content in the exhaust gases after they leave the combustion process of the engine. The oxygen sensor must be at a certain temperature in order for this information to be accurate. The oxygen sensor has a heater wire inside to help bring the sensor up to temperature quicker. When the PCM detects the heater wire is not operating, it will set code P0030.