O2 Heater Circuit

the O2 heater circuit is what makes 4-wire Oxygen Sensors different from 1-wire sensors. The heater circuit helps the sensor stay in its optimum temperature range so that it reads accurately. See One Wire To4 Wire O2 Sensor for information on adding circuitry to an ECU to support the O2 Heater Circuit. See the Rom Maps for information on diabling the code 41 present when it is absent/malfunctioning.