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. So HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions, which can operate closed loop fuel control or catalyst monitoring immediately upon engine start-up.
The ECM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the ECM provides a ground circuit for activating the heater.
If the current of HO2S’s heater is lower than 0.2A or higher than 3.5A, the ECM judged as a fault and DTC is set.
Item | Detecting Condition | Possible cause | |
DTC Strategy | ● Heater circuit current(AH) is monitored. | ● Poor connection ● Open or short in HO2S heater circuit ● Defective HO2S heater ● Defective ECM | |
Enable Conditions | ● Heater "ON". ● 11V ≤ Battery voltage ≤ 16V | ||
Threshold value | ● Circuit current, AH < 200mA or ● Circuit current, AH ≥ 3.5A | ||
Diagnosis Time | ● Continuous | ||
MIL On Condition | ● 2 driving cycles | ||
