This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles, including but not limited to Toyota, Dodge, Honda, Chevrolet, Hyundai, Nissan, etc. Specific repair steps may vary depending on the model. Essentially this P0031 code means that the resistance of the heater circuit is lower than normal. In most cases, that resistance level must fall below 0.8 A to trigger the DTC code.  There is also an oxygen sensor behind the converter which is Sensor #2.  The sensor is less effective when the exhaust gas temperature is low, so it includes a heater which is activated to help get better readings from the A/F O2 sensor.  This O2 sensor #1 may also be refered to as an air/fuel ratio sensor since on some vehicles it is. Causes A P0031 DTC trouble code may be A short or open in the heater circuit in the sensor A failed O2 sensor heater Wiring/connectors broken/frayed leading to sensor and/or relay Failed PCM/ECM Possible Solutions To fix a P0031 DTC code, you'll need to do a proper diagnosis. It detects the amount of oxygen in the exhaust gas compared to the outside air and then vehicle's computer adjusts the air/fuel ratio going into the engine.  Note, this code is very similar in nature to P0032, P0051, and P0052 Potential Symptoms Most likely you'll not notice any symptoms other than the MIL (malfunction indicator lamp, a.k.a. the check engine light) will illuminate.  To do that, you'll want to inspect the wiring and connectors leading to the sensor. Also if equipped with a heater relay and fuse, you'll want to check those as well.  check the ground circuit for continuity measure the resistance of the heater circuit (done on the sensor itself) measure the resistance and voltage of the wiring Refer to a service manual for the correct specifications (volts, ohms) for your vehicle. There's also a chance that replacement parts for the P0031 code may also fall under a federal emissions warranty (check with your dealer to see if it's covered).