Yes it the original 1.6L engine, and I actually have the Helm manual for my car. And yes you are correct it's the heater part of the O2 sensor that code 41 denoting. I was just generalizing it. I actually ran through part of the tests that the Helm manual suggested and didn't find any obvious problems. It did not have me check for continuity on heater wires of the O2 harness, but it did have me confirm that they were supplying 12V (well, battery voltage) when they should -- which should be just as good a check.

With my MPG notibly down and my Check Engine light indicating the O2 sensor (in general) I'm just going to get a new O2 sensor anyhow. I can get a universal Bosch one for $70 that I have to "splice" into the stock wiring (instead of spending $150-200 for the same sensor with a plug that fits the stock wiring).