Four wire O2 sensor

[Land Shark]

        EGO Sensors in a nutshell..

        1-Wire: Unheated, uses car body for signal return

        3-Wire: Heated, uses 2 wires for Heater and car body for signal return

        4-Wire: Heated, 2 wires for Heater and separate wire for signal return..

        Why?!? Diagnostics ground path testing!

        TIA,

        Jim C