Today I stopped by AutoZone to ask them to reset my CHECK ENGINE light, which I thought was old engine error code that I brought to FL from NH. But no, it turned out to be a new one — P0031.
A P0031 DTC (diagnostic trouble code) refers to the O2 sensor (oxygen sensor) located on Bank 1 in front of the catalytic converter. There is also an oxygen sensor behind the converter which is Sensor #2. More information.
Looks like this code doesn't just get reset. When reset, it comes back on immediately. This must definitely be O2 censor malfunction. 