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 HO2S’s signal is lean during power enrichment conditions, PCM sets P2197. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Monitor HO2S’s signal | ● Poor Connection ● Faulty HO2S ● Clogging of fuel filter in fuel pump ● Faulty PCM |
Enable Conditions | ● Battery voltage ≥ 10V ● Engine running ≥ 60sec. ● Power Enrichment conditions ● Engine warm-up state ● Not in Transient Conditions | |
Threshold value | ● HO2S’s signal < 0.35V and Air Fuel Ratio ≤ 13.5 | |
Diagnosis Time | ● Continuous (More than 8 sec. failure for every 9 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.
