Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR (HO2S)

INSPECTION







FUNCTION AND OPERATION PRINCIPLE
Heated Oxygen Sensor (HO2S) consists of zirconium and alumina and is installed on upstream and downstream of the Manifold Catalyst Converter (MCC). After it compares oxygen consistency of the atmosphere with the exhaust gas, it transfers the oxygen consistency of the exhaust gas to the PCM. When A/F ratio is rich or lean, it generates approximately 1 V or 0 V respectively. In order that this sensor normally operates, the temperature of the sensor tip is higher than 370 °C (698 °F). So it has a heater which is controlled by the PCM duty signal. When the exhaust gas temperature is lower than the specified value, the heater warms the sensor tip.

Specification:

SPECIFICATION

Waveform:

WAVEFORM

Fig1. The signal waveforms of front HO2S(the upper) and heater(the lower) at idle
Fig2. The signal waveforms of rear HO2S(the upper) and heater(the lower) at idle The HO2S request a minimum temperature to provide a closed loop fuel control system. So the HO2S contains a heater element to redrew its warm-up time and ensure its performance during all driving conditions. The PCM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.

Schematic Diagram:

SCHEMATIC DIAGRAM

COMPONENT INSPECTION
1. Check signal waveform of HO2S using a scantool.

Specification: Refer to "waveform".

2. Disconnect the HO2S connector.
3. Measure resistance between HO2S heater terminals 3 and 4.
4. Check that the resistance is within the specification.

Specification: Refer to SPECIFICATION.