Component Location
General Description
The heated oxygen sensors are mounted on the front side and the rear sied of Catalytic Converter (warm-up catalytic converter), which detects the oxygen concentration 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 heated oxygen snesor (HO2S) produces a voltage that varies between 0V and 1V. When the air/fuel ratio is lean, the oxygen concentration in the exhaust gas increases and the front HO2S outputs a low voltage (approximately 0 ~ 0.1 V).
When the air/fuel ratio is rich, the oxygen concentration in the exhaust gas decreases and the front HO2S output a high voltage (approximately 0.8 ~ 1 V). The ECM constantly monitors the HO2S and increases or decreases the fuel injection duration by using the HO2S signal, which is called closed-loop fuel control operation.
DTC Description
If the sensor output is over 1.08 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 B1S2 |
Enable Conditions | After enough heated
Battery voltage > 10.7V
Catalyst temperature (model) = 250~800?
|
Threshold Value | B1S2 sensor voltage > 1.08 V
|
Diagnostic Time | 5 sec.
|
MIL ON Condition | 3 driving cycle
|
? B1S1 : upstream oxygen sensor / B1S2 : 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.