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 oxygen sensor generates a voltage that indicates the difference between the oxygen content of the exhaust stream and the oxygen content of ambient air. When the exhaust stream is “rich,” there is more oxygen in the ambient air than in the exhaust stream, so the voltage will be higher.
Checking output signals from HO2S under detecting condition, if an output signal is below 0.04V for more than predeterminate time, PCM sets P0131. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Monitor signal voltage | ● Poor Connection ● Short to ground in harness ● HO2S(B1/S1) ● PCM |
Enable Conditions | ● Battery voltage ≥ 10V ● Engine running ≥ 60 sec. ● Engine warm-up state | |
Threshold value | ● The voltage of HO2S(B1/S1) < 0.04V | |
Diagnosis Time | ● Continuous (more than 12.5 sec. failure for every 15 sec.test) | |
MIL On Condition | ● 2 Driving Cycles |
Test Condition | HO2S Voltage(Sensor1) | HO2S Voltage(Sensor2) |
HO2S Signal at idle after warm-up | Signal is commonly switching from rich to lean more than 3 times in 10 sec. | Signal is commonly above 0.6V. |
HO2S signal at open circuit (Pumping current OFF) | Approx. 0.45V | |
HO2S signal at open circuit(Pumping current ON) | Approx. 3.5V |
After warming-up, if accelerator pedal is released suddenly around 4000rpm, the HO2S signal reading will be lower than 200mV resulting from Fuel cut-off for the moment. Conversely, if suddenly accelerator pedal is depressed, HO2S signal reading will be around 0.6V ~1.0V. At idle, Normally HO2S signal will switch from lean to rich with 3 Hz. And as racing, Its frequency rises.
