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When using a 4 wire sensor in place of aa original 3 wire , you have to be aware that a 4 wire heater circuit uses a seperate circuit..[which is the 2 white wires]
...so, in order for it to repalce the 3 wire , you have to hook one White to White , the other white to gray along with the gray [ ground], and Blk to Blk.
This will give you Blk for signal, gray for ground of both 02 and heater, and the other white for heater circuit feed .
The whites are not polarity sensitive, so either way is correct [ in other words , no +/- difference for heater white wires]