Oxygen Sensor: Description and Operation

Oxygen Sensor:

OXYGEN SENSOR (Non-heated)

Oxygen sensor is mounted in exhaust system where it can monitor oxygen content of exhaust gas. Oxygen content in exhaust reacts with sensor to produce a voltage output from approximately .1 volt (high oxygen content - lean mixture) to .9 volts (low oxygen content - rich mixture). Voltage can be measured with digital voltmeter having at least 10 Meg Ohms input impedance. Use of standard moving coil voltmeters will result in very inaccurate readings.

The oxygen sensor is made of zirconium dioxide ceramic. Both inner and outer surfaces are coated with a thin layer of platinum. The sensor is installed in the exhaust manifold so that the inner surface is exposed to exhaust gases and the outer surface is in contact with outside air. The difference in the amount of oxygen contacting each surface results in voltage being generated. The ECM interprets the voltage signal as either rich or lean and makes appropriate air/fuel ratio adjustments. ECM adjustments are rapid and continuous while the system is operating in "Closed Loop." To operate properly, the oxygen sensor must be thoroughly warmed up.

Oxygen sensor circuit, if open, should set Code 13. Constant low voltage in circuit should set Code 44. Constant high voltage in circuit should set Code 45.

Codes 44 and 45 could also be set by as a result of fuel system problems. Be sure to refer to code charts for conditions causing rich / lean system.

Oxygen Sensor:

OXYGEN SENSOR (Heated)

Heated oxygen sensor operation is same as non-heated sensor. The difference is that B+ is supplied to a heating unit that is part of sensor. Heater receives voltage from charging circuit and helps ECM control fuel injection sooner for better fuel emissions.

There are no malfunction Codes to detect if heater part of sensor is not working.