Oxygen Sensor: Testing and Inspection

Circuit Diagram

Troubleshooting Hints
- If the HO2S is defective abnormally high emissions may occure.
- If the HO2S check has resulted normal but the sensor output voltage is out of specifications, check for the following items related to air fuel ratio control system.
- Faulty injector
- Air leaks in the intake manifold.
- Faulty volume air flow sensor, intake air temperature sensor, barometric pressure sensor, engine coolant temperature sensor.





Using scan Tool











Harness Inspection Procedure

Sensor Inspection

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





1. Disconnect the oxygen sensor connector, and measure the resistance between terminal 3 and terminal 4.





2. Replace the oxygen sensor if there is malfunction.
3. Apply battery voltage directly between terminal 3 and terminal 4.

NOTE: Take care when applying the voltage, because damage will result if the terminals are incorrect or are short circuited.

4. Connect a digital-type voltmeter between terminal 1 and terminal2.
5. While repeatedly racing the engine, measure the oxygen sensor output voltage.





6. If there is a problem, it is probable that there is a malfunction of the oxygen sensor.