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 800mV when the air fuel ratio is richer than the theoretical ratio and output of about 100mV 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.
If the heated oxygen sensor is defective, abnormally high emissions may occur.
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. |
Check item | Check condition | Engine condition | Test specification |
Heated oxygen sensor output voltage | Warm-up | When decelerating suddenly from 4000 rpm | A. 200mV or lower |
When engine is suddenly raced | B. 600 ~ 1000mV |
If you release the accelerator pedal suddenly after engine running about 4000 rpm, fuel supply will stop for short period and the O₂sensor service data in the HI-SCAN will display values in the A range.
When you suddenly press on the acclerator 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 O₂sensor can be determined as good.
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.
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)
