Oxygen Sensor: Testing and Inspection

TROUBLESHOOTING PROCEDURES




CIRCUIT DIAGRAM











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.
Replace the oxygen sensor if there is a malfunction.

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

Resistance: @ 400°C (752°F) 30 or more Ohms

2. Replace the sensor if not as specified.

Tightening torque: 50-60 Nm (37-44 lb.ft.)

Voltage Inspection




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.


TROUBLESHOOTING HINTS
- When the lean/rich period is above 2.6 seconds in the condition that fully warm-up engine is 2,000-3,000 rpm and engine is above middle load.
- If the heated oxygen sensor is detective abnormally, high emissions may occur.
- 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.

- When O2 sensor output voltage is maintained as following for above 50 sec.

- Upstream: 0.4V-0.6V
- Downstream: 0.4V-0.5V