The rear heated oxygen sensor is mounted on the rear side of the Catalytic Converter (warm-up catalytic converter) or in the rear exhaust pipe, which is able to detect catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0V and 1V. This rear heated oxygen sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.
Checking output signals from HO2S every 15 sec. under detecting condition, if an output signal is above 1.3V for more than 12.5 sec. PCM sets P0138. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Signal high | ● Poor connection ● Short to battery in harness ● HO2S(B1/S2) ● PCM |
Enable Conditions | ● Battery voltage ≥ 10V ● The minimum airflow ≥ 2g/s ● Engine running state ≥ 60 sec. ● The coolant temperature ≥ 60°C(140°F) ● Feed-back control(Closed loop) state ● No fuel-cut state ● Above conditions are met > 5 sec. ● HO2S heated state ● No transient condition | |
Threshold value | ● The voltage of HO2S(B1/S2) > 1.3V | |
Diagnosis Time | ● Continuous (More than 12.5 sec.failure for every 15 sec.test) | |
MIL On Condition | ● 2 Driving Cycles |
Air/fuel mixture | Voltage(V) |
Rich | 0.75 ~ 1V |
Lean | 0 ~ 0.12V |
