2002 Mazda MPV P0031 O2 Sensor Heater Circuit Low - Diagnosis and Causes

The check engine light has activated on my 2002 Mazda MPV with a 6-cylinder 3.0L engine, currently at 114,500 miles. I first checked the gas cap as it had just been refilled, but the warning light did not turn off. The vehicle has been running smoothly without any performance issues. After driving approximately 250 miles, I visited an AAA garage to retrieve diagnostic codes and found P0031: Heater Control Circuit Low for Oxygen Sensor (HO2S), Bank 1, Sensor 1. This code suggests a potential issue with the heater circuit of the oxygen sensor, which could indicate a faulty O2 sensor or related wiring problems. I was advised that while this condition does not require immediate action, further diagnosis is necessary to confirm the root cause. I made a second trip of about 250 miles after refilling the tank, and the check engine light remains on—vehicle performance is still normal. Given these symptoms, is it likely that the O2 sensor is at fault? Are there other possible causes such as wiring issues, connector corrosion, or faulty sensors in the heater circuit? Any insights from owners of this model who have experienced similar problems would be greatly appreciated. Thank you, RichN