The oxygen sensor itself has a heater, to make sure its element stays over
750F. Below that temperature it begins to lose effectiveness.

Oxygen sensors need to be above 500F to start working, and to be at 750F to
be fully effective. Old-style single-wire oxygen sensors relied on the
exhaust gas itself to heat them up. As legislated emissions limits dropped,
this method became inadequate, so a heater was added to the sensor body,
along with dedicated ground wires to ensure electrical integrity.

But doesn't this car have a A/F sensor rather than an O2 sensor? If so, the
heater is even more necessary. A/F sensors run at 1,500F, a temperature
impossible to maintain relying on exhaust heat alone.