Heated Oxygen Sensor 1 (HO2S 1)

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DESCRIPTION
The Heated Oxygen Sensor 1 (HO2S 1) is mounted in the exhaust pipe below the exhaust manifold, where it can detect the concentration of oxygen in the exhaust gases. The HO2S 1 consists of the zirconia element (with a thin platinum surface coating) which generates an electromotive force, a lead wire which draws out the electromotive force, a heater which promotes activation of the zirconia element, lead wires for the heater power and ground circuits and a cover and housing which protects the zirconia element from damage.



OPERATION
The zirconia element, by its property, generates an electromotive force when a difference in oxygen concentration exists between its faces. As its temperature rises, the change of the electromotive force is amplified by the catalytic reaction of the platinum. The HO2S makes use of this property. Atmosphere is introduced into the HO2S. The inside of the zirconia element is exposed to the atmosphere and the outside to exhaust gases. The difference in concentration between the inside and the outside of the zirconia element varies with the oxygen concentration in the exhaust gases. A large difference in concentration results in about 1 volt of electromotive force while a small difference results in about 0.01 volt.

This voltage should constantly fluctuate from approximately 1O00mV (high oxygen content - lean mixture) to 9OOmV (low oxygen content - rich mixture). By monitoring the voltage output of the oxygen sensor, the PCM calculates what fuel mixture commands to send to the fuel injectors (lean mixture-low HO2S voltage=rich command, rich mixture-high HO2S voltage=lean command). The oxygen sensor voltage can be monitored with a scan tool.

The oxygen sensor's ability to provide accurate and useful voltage signals can be affected by the presence of certain contaminants. The contaminants can be introduced through the fuel system or can be air born. Some of the contaminants that may be encountered are phosphorus, lead, silica, and sulfur. One of the more common contaminants is silica in the from of silicone. Silicone contamination may be indicated by a white powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. Silicone contamination can be caused by the use of gasoline with silicone in it or by the use of RTV sealants which emit silicone into the crankcase or induction system. Oxygen sensors exposed to high concentrations of engine coolant or engine oil in the exhaust stream can also be adversely affected.