For those wondering what the code means...
P0031 - HO2S Heater Control Circuit Low
In English it means the O2 Sensor is not heating up as fast as it should. There is a pre-heat function that brings the O2 sensor up to operating temp faster in order to reduce emissions.
There could be a bad wire, lose plug or the O2 sensor might need to be replaced. This does only effect the warm-up. Once the sensor is heated to operating temps by the exhaust then all is good emissions wise again.
