Oxygen Sensor: Testing and Inspection

HEATED OXYGEN SENSOR (HO2S) - ZIRCONIA (Z(r) O(2))




The heated oxygen sensor (HO2S) senses the oxygen concentration in exhaust gas and converts it into a voltage that is sent to the ECU. For Zirconium type sensors, 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 ECU controls the fuel injection ratio based on this signal so that the air fuel ratio is maintained at the stoichiometric ratio. The oxygen sensor has a heating element that ensures sensor performance during all driving conditions.

Circuit Diagram (HO2S):

Harness Connector:

HO2S - ZIRCONIA (Z(r) O(2)) OPERATION PRINCIPLE




The Zirconia (Z(r) O(2)) which is coated with Platinum (Pt) on both sides will generate the voltage if the density of oxygen on atmosphere side and exhaust gas side is different in high temperature.

In other words oxygen ion moves from high-density side (Atmosphere) to low-density side (exhaust gas), at a result Sensor Voltage is generated by Nearest equation between two electrodes.

TROUBLESHOOTING HINTS

1. If the HO2S is defective, abnormally high emissions may occur.
2. If the HO2S check results are normal, but the sensor output voltage is out of specification, check for the following items (related to air fuel ratio control system):

1. Defective Injector
2. Air leaks in the intake manifold
3. Defective Mass Air Flow (MAF) Sensor
4. Defective Intake Air Temperature Sensor (ATS)
5. Defective Water Temperature Sensor (WTS)
6. Defective Manifold Absolute Pressure (MAP) Sensor

SENSOR INSPECTION (HO2S)




1. USING HI-SCAN (PRO)
2. USING VOLTMETER

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 Heated Oxygen Sensor (HO2S) connector, and measure the resistance of heater between terminal 3 and terminal 4.

HO2S (Bank 1, Sensor 1): 3.3 Ohm
HO2S (Bank 2, Sensor 1): 3.3 Ohm
HO2S (Bank 1, Sensor 2): 6.0 Ohm
HO2S (Bank 2, Sensor 2): 6.0 Ohm

2. Replace the Heated Oxygen Sensor (HO2S) if there is a malfunction.
3. Apply battery voltage directly between terminal 3 and terminal 4.

NOTE: Be careful when applying the voltage. Damage will result if terminals 1 and 2 are connected to any voltage.

4. Connect a high-impedance digital-type voltmeter between terminal 1 and terminal 2.
5. While repeatedly racing the engine, measure the Heated Oxygen Sensor (HO2S) output voltage.
6. If there is a problem, replace the Heated Oxygen Sensor (HO2S).

Tightening torque: 40 - 50 Nm (4 - 5 kg.m, 29 - 36 lb.ft)

Harness Inspection Procedures (HO2S):