Ok, I understand the what you said now about the .46V and it makes sense, but I wanted to be sure the view was clear. The 1/2 volt you saw is deceivingly close to the value one might expect on the sensor's output lead, while connected to the ECU and not yet warm. But it could also represent the voltage developed across the wiring to wherever the Camaro's heater lead gets its ground return. In other words, the .46V says the heater is connected and drawing current. To double-check that, simply disconnect the heater's battery source, and that .46V should drop to nearly zero.

Now about the heater working key-on, I didn't know that it would. An LH2.4 Volvo needs to have the motor running (or cranking) to heat the sensor. No matter, though, the earlier Volvos' oxygen sensors got heated with key on.
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Art Benstein near Baltimore

Acupuncture is a jab well done.