Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR (HO2S)- SINGLE HO2S
The heated oxygen sensor senses the oxygen concentration in the exhaust gas, then converts it into a voltage and then sends this to the ECM. The heated oxygen sensor gives an output of about 800 mV when the air fuel ratio is richer than the theoretical ratio and output of about 100 mV when the ratio is leaner (higher oxygen concentration in exhaust gas.) The ECM controls fuel injection based on this signal so that the air fuel ratio is maintained at the theoretical ratio.

Circuit Diagram:

TROUBLESHOOTING HINTS
1. If the heated oxygen sensor is defective, abnormally high emissions may occur.
2. If the heated oxygen sensor check is normal but the sensor output voltage is out of specification, check for the following items related to the air fuel ratio control system:
- Faulty injector.
- Air leaks in the intake manifold.
- Faulty mass air flow sensor, purge valve and engine coolant temperature sensor.
- Wiring connection problem.

Using Voltmeter/Hi-Scan:

NOTE:
If you release the accelerator pedal suddenly after engine running about 4000 rpm, fuel supply will stop for short period and the O2 sensor service data in the HI-SCAN will display values in the A range.

When you suddenly press on the accelerator pedal down, the voltage will reach B range.
When you let the engine idle again, the voltage will fluctuate between ranges A and B. In this case, the O2 sensor can be determined as good.

Harness Inspection Procedure:

SENSOR INSPECTION

NOTE:
1. Before checking, warm up the engine until the engine coolant temperature reaches 80 to 95 °C (176 to 20 °F).
2. Use an accurate digital voltmeter.
Replace the oxygen sensor if there is a malfunction.

Tightening torque
Heated oxygen sensor : 50 - 60 Nm (500 - 600 kg.cm, 37 - 44 lb.ft)