Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR (HO2S) - (Dual HO2S)
The heated oxygen sensor senses the oxygen concentration in the exhaust gas and, converts it into a voltage which is sent to the ECM. The heated oxygen sensor outputs about 800 mV when the air fuel ratio is richer than the theoretical ratio and outputs about 100 mV 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 heater element which ensures the sensor performance during all driving condition.

Circuit Diagram:

Troubleshooting Procedures Part 1:

Troubleshooting Procedures Part 2:

Troubleshooting Hints:

TROUBLESHOOTING HINTS
1. If the heated oxygen sensor is defective abnormally, high emissions may occur.
2. If the heated oxygen sensor check has been normal, but the sensor output voltage is out of specification, check the following items related to the air fuel ratio control system.
- Faulty injector.
- Air leaks in the intake manifold.
- Faulty mass air flow sensor, EVAP valve and engine coolant temperature sensor.
- Wiring connection problem.
3. When O2 sensor output voltage is maintained as following for above 50 sec.
- Upstream 0.4 V - 0.6 V
- Downstream : 0.4 V - 0.5 V

Using Voltmeter:

NOTE: If you release the accelerator pedal suddenly with the engine running about 4000 rpm, the fuel supply will be stopped for a while.

When you suddenly press the accelerator pedal, the voltage will reach 'B' range. Then, when you let the engine idle again, the voltage fluctuates between 'A' and 'B' range. In this case, the O2 sensor can be determined as good.

Harness Inspection Procedures:

SENSOR INSPECTION

NOTE
1. Before checking, warm up the engine until the engine coolant temperature reaches 80 to 95 °C (176 to 205 °F).
2. Use an accurate digital voltmeter.




1. Disconnect the heated oxygen sensor connector, and measure the resistance between terminal 3 and terminal 4
2. Replace the oxygen sensor if there is a malfunction.
Heated oxygen sensor : 50 - 60 Nm (500 - 600 kg.cm, 37 - 44 lb.ft)