Zirconium Dioxide Oxygen Sensor Operating Characteristics

Air/ Fuel Ratio

Exhaust Oxygen Concentration

Ambient Oxygen Concentration

Electron Concentration

Signal Voltage

Rich

Low

High

Positive plate

High

Lean

High

High

Positive and Negative plates

Low

Zr02 sensor voltage signal and ECU processing: The voltage signal produced by. the oxygen sensor is relatively small. During the richest operating conditions, this signal approaches 1000 millivolts (1 volt).

The Zr02 oxygen sensor is wired as shown in the diagram. Voltage characteristics are depicted in the accompanying graph.

As the voltage graph illustrates, the output of the Zr02 sensor acts almost like a switch. As the air/fuel ratio passes through the stoichiometric range, voltage rapidly switches from high to low.

The ECU comparator circuit is designed to monitor the voltage from the sensor and send a digital signal to the microprocessor. If sensor voltage is above the comparator switch point, z 1/2 volt, the comparator output will be high. If the sensor voltage is below the comparator switch point, the comparator output will be low. The microcomputer monitors the output of the comparator to determine how much oxygen remains in the exhaust stream after combustion occurs.

Zr02 Sensor Circuit

Titania Oxide Sensor This four-terminal device is a variable resistance sensor with heater. It is connected in series between the OX+ reference and a fixed resistance located inside the ECU. This circuit operates similarly to a thermistor circuit.

The properties of the thick film titania element are such that as oxygen concentration of the exhaust gas changes, the resistance of the sensor changes. As the sensor resistance changes, the signal voltage at the ECU also changes.

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