The HO2S is used to supply the PCM with information regarding the composition of the air/fuel mixture. The HO2S is positioned in the exhaust pipe ahead of the TWC. To measure the oxygen content, the HO2S requires a supply of ambient air as a reference. Since this is supplied through the wiring, the lead must not be clamped or damaged in any other way. The HO2S produces a voltage that varies between 0.1V and 0.9V under normal operating conditions. The Engine Control Module (PCM) monitors this voltage and determines if the exhaust gas is lean or rich. If the voltage input at the PCM is under approx. 0.45V the exhaust is lean, and if the voltage input is over approx. 0.45V the exhaust is rich. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary.
The PCM monitors front oxygen sensor amplitude level and compares it to predetermined minimum amplitude value which could increase emission or disturb lambda control by the effect of aging on the oxygen sensor. The PCM sets DTC P0133 when the amplitude of oxygen sensor is equal to or less than minimum amplitude threshold.
Item
Detecting Condition &
Possible Cause
DTC Strategy
? Comparison of O2 sensor lean/rich period with calculated period
? Leak in intake or exhaust system
? Faulty fuel system.
? Front and rear HO2S connections reversed.
? Contact resistance in connectors
? HO2S contamination
Enable Conditions
? Coolant temp. > 74°C(165?)
? 400°C(752?) < Catalyst temp. model < 900°C(1652?)
? 5km/h(3MPH) < Vehicle speed < 180km/h(112MPH)
? Engine speed < 3400rpm
? 200 < Engine load(mg/rev.) < 700
? 11V < Battery voltage
? Stable driving condition
? Lambda regulation active
? Canister Purge Valve not in CLOSE state
Threshold Value
? Average Ratio between measured and maximum allowed frequency during 100 Lambda regulation cycles > 1
Diagnostic Time
? 100 lambda controller cycles
Fail Safe
? Reset lambda adaptation and fuel trim adaptation
? Front HO2S heater is controlled in open loop control
? EVAP. Emission control function is controlled in minimum operation mode