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.
ECM assumes that O2 sensor heater coil is abnormal and shows P0135 when the corrected resistance value of upstream O2 sensor heater is higher than the specification.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Signal check | 1. Poor connection 2. Open or Short to ground in power circuit 3. Open in control circuit 4. S1 |
Enable Conditions |
•
Exhaust Gas temperature > 450°C
•
Heating period > 50sec
•
Battery voltage : 10.7V ~ 16.1V | |
Threshold Value |
•
Internal resistance > Threshold value (Calculated by exhaust gas temp. or heating power) | |
Diagnostic Time |
•
60sec | |
MIL ON Condition |
•
3 driving cycle |
※ S1 : upstream oxygen sensor / S2 : downstream oxygen sensor
ITEM | Specification |
Heater Resistance(Ω) | Approx. 9.0Ω at 20℃ (68℉) |
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.