The sensor you got the code from is the one that is closest to the oil flter. It is in the exhaust manifold, just before the y-pipe (at the front of the engine). It's one of the "after car" (downstream) sensors, so its malfunction won't effect driveability of the car in any way. It's more of an emissions monitor than anything else.
It is really easy to replace that one. Your problem is one of three things: A) a faulty heater circuit in the O2 sensor itself (could be, fixed by replacing the sensor), B) a bad connection at the O2 connector (could be, can be fixed by cleaning the connector pins - FREE), or C) some sort of open or short in the wires themselves leading from the PCM to the O2 sensor (least likely and most difficult to track down).
Try B first, then A, then C if a new sensor doesn't fix the problem.
