Component Location
General Description
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.
DTC Description
If the sensor output is over 4.5 V under enable conditions, ECM sets DTC P0138.
( This DTC might be caused by the malfunction of Heater circuit, so, check the heater circuit first. )
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | Signal check, high
| Poor connection Short to power in signal circuit S2 |
Enable Conditions | IG ON
Battery voltage 10~16V
Engine speed = 500 rpm
70? = Coolant temperature < 150?
Intake air temperature : -10~80 ?
atmospheric pressure > 75 kPa
|
Threshold Value | S2 sensor voltage > 4.5 V
|
Diagnostic Time | 37.5 sec
|
MIL ON Condition | 3 driving cycle
|
? S1 : upstream oxygen sensor / S2 : downstream oxygen sensor
Diagnostic Circuit Diagram
Signal Waveform & Data
If you release the accelerator pedal suddenly after engine running about 4000 rpm, fuel supply will stop for short period and the O2 sensor service data in the Hi-Scan (Pro) will display values 200mV or lower. When you suddenly press on the accelerator pedal down, the voltage will reach 0.6 ~ 1.0 V. When you let the engine idle again, the voltage will fluctuate between 200 mV or lower and 0.6 ~ 1.0 V. In this case, the O2sensor can be determined as good.