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.
If ECM detects that the internal resistance of heater is out of threshold value, ECM sets DTC P0135.
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Heater current check | ● Poor connection ● Open or short to ground in control circuit ● B1S1 |
Enable Conditions | ● Exhaust gas temperature (model) : 200∼575 ℃ ● Intake air temperature > -6 ℃ ● Battery voltage 10.7∼16.1 V | |
Threshold Value | ● Internal resistance > threshold f(exhaust gas temp., heater power) | |
Diagnostic Time | ● Above 15 sec | |
MIL ON Condition | ● 2 driving cycle |
※ B1S1 : upstream oxygen sensor / B1S2 : downstream oxygen sensor
ITEM | Specification |
Heater Resistance | Approx. 9.0Ω |
