What Is a Heater Circuit in an O2 Sensor?


The oxygen or O2 sensor in your vehicle helps your computer monitor the operating conditions of the fuel injection system to reduce harmful emissions. However, the sensor can only do its job once it has reached operating temperature. With a heater circuit, your vehicle's computer can reduce air pollution by getting the O2 sensor up to speed soon after you fire up your engine.

Heater Circuit in an O2 Sensor

  • Many late-model vehicles come equipped with oxygen sensors that have an integrated electric heating element. Electrical energy heats up this element inside the heated oxygen sensor (HO2S) so that it can start operating sooner, as compared to oxygen sensors without a heating element, to reduce air pollution. Moreover, once the HO2S reaches operating temperature, the computer in your vehicle's fuel injection system is able to enter a closed loop.

Open and Closed Loops

  • The computer in your vehicle uses the HO2S and other sensors to determine the best air/fuel ratio for the engine operating conditions at any given moment. However, when you fire up your engine first thing in the morning, the computer operates in an open loop, ignoring the HO2S and other sensor signals because they are not at operating temperature. Since the heating element in your oxygen sensor allows it to warm up, it helps the computer go into a closed loop sooner for better emissions control.

The Job of the HO2S

  • The oxygen sensor in your vehicle is in charge of reading the oxygen content in the exhaust stream as it leaves the engine, enters the exhaust manifold and travels down the tail pipe. The computer receives an electrical signal from the sensor with this information and uses it to adjust the rate of fuel sent to the combustion chambers to reduce the production of hydrocarbons, carbon monoxide, oxides of nitrogen and other harmful emissions.

Zirconia Oxygen Sensors

  • If you have installed a zirconia oxygen sensor in your vehicle, most likely it is a heated oxygen sensor type. Zirconia, a white crystalline oxide, is the active material used in many of these sensors to produce the voltage signals sent to the computer. Zirconia operates at optimal efficiency in temperatures of about 600 Fahrenheit.

How Your Zirconia Sensor Works

  • Oxygen sensors are about the size of a spark plug and sit between the exhaust manifold and the catalytic converter. With the engine running, the heated oxygen sensor takes a sample of the oxygen content in the atmosphere and compares this sample to the amount of oxygen in the exhaust stream. The difference of oxygen in both samples lets the sensor produce a voltage signal. The computer compares this voltage signal to the value stored in memory to determine the correct amount of fuel to send to the combustion chambers.

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  • "Modern Automotive Technology"; James E. Duffy; 2003
  • "The Haynes Emissions Control Manual"; Mike Stubblefield and John H. Haynes; 2001
  • Photo Credit Hemera Technologies/AbleStock.com/Getty Images
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