Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR (HO2S)




The heated oxygen sensor senses the oxygen concentration in exhaust gas, converts it into a voltage, which is sent to the ECM. The oxygen sensor outputs about 1 V when the air fuel ratio is richer than the theoretical ratio, and outputs about 0 V when the ratio is leaner (higher oxygen concentration in exhaust gas.). The ECM controls the fuel injection ratio based on this signal so that the air fuel ratio is maintained at the theoretical ratio. The oxygen sensor has a heating element which ensures the sensor performance during all driving conditions.

Configuration And Circuit Diagram:

The basic principle of the operation of titania sensor is that, when the oxygen concentration from the exhaust emission manifold reduces (RH) , the volume of O2 and the electronic concentration value will increase to make the titania element resistance reduce and, reversely, when the oxygen concentration increases (leaner), the resistance will increase. Accordingly, the ohm value of above 100 kOhms is regarded as corresponding leaner condition and the value below 100 kOhm as richer condition.

The main point to check the oxygen sensor output function is to check the output voltage for being 0.1 - 0.9 V and the frequency 1.1 Hz at the engine rate of 3000 rpm after full warming up.

The point of service is to check that the frequency is about 1.1 Hz while checking the output is also important.

Troubleshooting hints
1. Excessive exhaust gas will be emitted when the oxygen sensor is faulty.
2. Check the parts as below when the sensor output value is out of the specified range even though the sensor is in normal condition.
- Incomplete injector
- Air leakage from intake manifold
- Incomplete air flow sensor, intake air temperature sensor and engine coolant temperature sensor.
- Exhaust leakage

Using GST:

INSPECTION (USING VOLTMETER)

NOTE: Warm up the engine up to the extent that the engine coolant temperature reaches 80 - 95°C (176 - 203°F) prior to start the check.

1. Directly apply the battery voltage between terminal 4 and 3.

NOTE: Be sure to correctly apply the voltage since any incorrect connection or a short circuit may destroy the system.

2. Use a digital voltmeter to connect between terminal 2 and 1.




3. Measure the oxygen sensor output voltage during running the engine continuously.

4. If there is any abnormality, it may be caused from the oxygen sensor.

Tightening Torque
Heated oxygen sensor : 28.9 - 36.2 lb.ft (400 - 500 kg.cm)

Harness Inspection Procedures: