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 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.
When ECM detects the open in the heater control circuit(B1S2), ECM sets DTC P0036.
Item
Detecting Condition
Possible Cause
DTC Strategy
Heater check open
Poor connection
Open or short to ground in power circuit
Open in control circuit
B1S2
Enable Conditions
-
Threshold Value
Diagnostic Time
Continuous
MIL ON Condition
3 driving cycle
Specification
Heater Resistance(?)
Approx. 9.0? ( 20?)
Fig.1) The signal waveforms of rear HO2S(B1/S2) and heater(the lower) at idle.