What does Diagnostic trouble code p0031 ho2s heater control circuit low bank 1 sensor 1 on a 2002 suzuki xl7 refer to and where is this sensor located on the engine?

Most likely a bad O2 sensor. Search the net for O2 sensor info for how they work and more detail on heated O2 sensors. Sensor 1 means upstream or in the manifold. In front of the catylytic converter. There is what appears to be a small catylytic converter at the very end of the exhaust manifolds in addition to the one that looks like a normal size converter. Sensor one is at the back of the exhaust manifold between the enging and the manifold. I don't know which side is bank 1 as I got here looking for that info myself. Best info I have is it's the side with the number one cylinder, but I don't know whether it's the left or right. Reference source: http://www.aa1car.com/library/o2sensor.htm