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 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.
This oxygen sensor varieties use a “bias” voltage to achieve better resolution of the exhaust stream signal. Some oxygen sensor varieties use a “pumping circuit” to force ambient air into the sensor to maintain a more pure environment for comparison. In either case, a cold sensor will tend to indicate voltage values near the open circuit value. For the “pumping current” sensors, this open circuit value can be near 3.5 V. Since the Fuel control logic would incorrectly consider this reading to indicate a very rich mixture for an extended time, the fuel control logic can not use the oxygen sensor reading under such conditions.
The PCM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.
DTC Description
Checking output signals from HO2S under detecting condition, if an output signal within the detecting condition lasts continuously, PCM sets P2198. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition
Item | Detecting Condition | Possible cause |
DTC Strategy | ? Determines if O2 sensor indicates rich exhaust while in decel fuel cut-off | ? Poor Connection ? Faulty HO2S ? Faulty PCM |
Enable Conditions | ? Sensor not in cooled status ? Not in Transient Conditions status ? Airflow present = 2 g/s ? Ignition voltage = 10V ? Fuel reduction not active ? Engine running ? Engine running long enough = 60sec. ? Deceleration Fuel cut off conditions present ? Engine coolant warm enough = 60°C( 140 °F) ? Above conditions met long enough = 1sec. |
Threshold value | ? O2 sensor voltage > 0.4199V |
Diagnosis Time | ? Contineous (More than 11.25sec. failure for every 12.5sec. Test) |
MIL On Condition | ? 2 Driving Cycles |
Schematic Diagram