The HO2S(Heated Oxygen Sensor) 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 the HO2S(B1/S1) transition frequency for predetermined time. During the monitoring period, the PCM calculates transition times that the front HO2S switches from rich to lean and from lean to rich. With this information, an average frequency for all switches can be determined. The PCM sets DTC P0133 when the average frequency is too slow.
Item
Detecting Condition
Possible Cause
DTC Strategy
Check Lambda control regulation frequency
Leak in intake or exhaust system
Poor connection or damaged harness
HO2S contamination
Enable Conditions
Coolant temperature >73?(163?)
550?(1022?)< Catalyst temperature model <850?(1562?)
Vehicle speed >3mph
1300< Engine speed(rpm) <3200rpm
0.3g/rev.< MAF <0.8g/rev.
Canister load <0.5
Lambda control active
Stable driving condition
No opening/closing of canister purge valve
70kPa(700hPa)< Ambient pressure
No relevant failure
11V< Battery voltage <16V
Threshold Value
Average Ratio between measured and maximum allowed frequency >1
Diagnostic Time
50 lambda controller cycles
Mil On Condition
2 Drive Cycles
? Sector A : Before Oxygen Sensor(B1S1) activated
? Sector B : Normal signal of Oxygen Sensor(B1S1) during idle
? Sector C : Line break in signal circuit