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. The HO2S produces a voltage that varies between 0.1V and 0.9V under normal operating conditions. The Powertrain 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 response time of an O2 sensor can be impacted by two factors: temperature and poisoning. Poisoning of the O2 sensor is the primary failure mode of O2 sensor response time. Poisoning can come from many sources: silicone from gaskets or even in the fuel, phosphorous from engine oil, carbon from operating in a cooler environment or lead from the fuel. Most poisoning failures have the potential to clear up after the source of the poisoning has been removed. However, sometimes the poisoning may be so severe that the damage is irreversible.
Checking output signals from HO2S under detecting condition, if an output signal is out of threshold, PCM sets P0133.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Determines O2 sensor functionality by checking its response rate | ● Poor connection ● Faulty HO2S ● Faulty PCM |
Enable Conditions | ● 1200 ≤ Engine RPM ≤ 4300 ● 7.5g/s ≤ Air Flow ≤ 40g/s ● Engine run time >60sec ● Engine Coolant > 70°C( 158 °F) ● No Decel Fuel Cut-Off Exit with Rich Bias Fueling ● No torque Fuel Reduction in effect ● No Disabling Faults ● All of the conditions above met for more than 2 sec. | |
Threshold value | ● Switching counter lean to rich < 13 ● Switching counter rich to lean < 13 ● Response Lean Rich Transition Counter/Response Lean Rich Switch Counter > 29 ● Response Rich Lean Transition Counter/Response Rich Lean Switch Counter > 35 ● Response Rich Lean Average/Response Lean Rich Average < 0.3809 ● Response Rich Lean Average/Response Lean Rich Average > 3 | |
Diagnosis Time | - | |
MIL On Condition | ● 2 Driving Cycles |
HO2S | Response Time (70% Duty at 10Hz) |
lean to rich( Less than 65ms) rich to lean(Less than 80ms) |
