In order to control emissions of the CO, HC and NOx components of the exhaust gas, heated oxygen sensor (HO2S), mounted on the front side and rear side of catalytic converter, detects the oxygen content in the exhaust gas. The front HO2S signal is used to control air/fuel ratio (closed loop fuel control) and the rear HO2S signal is used to monitor front HO2S and catalyst for proper operation.
The HO2S requires a minimum temperature to operate properly and provide a closed loop fuel control system. The HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions.
The oxygen sensor generates a voltage that indicates the difference between the oxygen content of the exhaust stream and the oxygen content of ambient air. When the exhaust stream is “rich,” there is more oxygen in the ambient air than in the exhaust stream, so the voltage will be higher.
Checking output signals from HO2S every 90 sec. under detecting condition, if an output signal indicating open in the circuit lasts for more than 76.5 sec., PCM sets P0154. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Open | ● Poor connection ● Open in harness ● HO2S(B2/S1) ● PCM |
Enable Conditions | ● No sensor cooled status ● The minimum airflow ≥ 2g/s ● The battery voltage ≥ 10V ● Engine running state > 60 sec. ● Coolant temperature ≥ 60°C(140°F) ● No fuel reduction ● No transient condition ● No fuel-cut state ● No disabling fault | |
Threshold value | Case 1 | ● At pumping current ON ● 1.2V ≤ Voltage of HO2S ≤ 3.9V |
Case 2 | ● At pumping current OFF ● 0.415V ≤ Voltage of HO2S ≤ 0.515V | |
Diagnosis Time | ● Continuous (More than 76.5 sec.failure for every 90 sec.test) | |
MIL On Condition | ● 2 driving cycles |
Air/fuel mixture | Voltage(V) |
Rich | 0.75 ~ 1V |
Lean | 0 ~ 0.12V |
※In case of open circuit, voltage is set to 0.45V(Pumping current OFF) or 3.5V(Pumping current ON)
