In order to control the emission of the CO, HC and NOx components of the exhaust gas, a heated oxygen sensor (HO2S), mounted on the front side and rear side of the 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 the HO2S contains a heater element to reduce warm-up time and ensure proper performance during all driving conditions, which allows for 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.
The ECM determines rear HO2S heater fault and sets DTC P0036 if measured rear HO2S resistance is lower than the predetermined threshold. The ECM illuminates the MIL on the second consecutive driving cycle that the diagnostic runs and fails.
Item
Detecting Condition
Possible Cause
DTC Strategy
Signalcheck
Contact resistance in connections.
Open or Short in power circuit
Open or Short in control circuit
Faulty HO2S(DOWN)
Faulty ECM
Enable Conditions
IG ON
Threshold Value
Wire disconnection
Diagnostic Time
Continuous
MIL ON Condition
3 driving cycle
Temperature
Frone HO2S Heater Resistance
20 ?
9.0 ?
The HO2S requires a minimum temperature to provide a closed loop fuel control system. So the HO2S contains a heater element to reduce its warm-up time and ensure its performance during all driving conditions. The HO2S heater is controlled ON after engine start except for Cold condition and high speed accelleration. 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.