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.
If the HO2S signal’s response time from lean to rich is longer than 1.2 seconds or from rich to lean is longer than 0.5 seconds, the PCM determines that a fault exists and a DTC is stored.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Response time from lean to rich (TLR) & from rich to lean (TRL) are monitored when A/F is intentionally changed. | ● Poor connection ● Leak in exhaust system ● Faulty HO2S ● Faulty PCM |
Enable Conditions | ● Closed loop | |
● Engine coolant > 49℃ | ||
● 1200rpm < Engine speed < 3000rpm | ||
● 25% < Load value < 60% | ||
Threshold value | ● From lean to rich (TLR) > 1.2 sec | |
● From rich to lean (TRL) > 0.5 sec | ||
Diagnosis Time | ● 8 sec |
Response times | Normal parameter |
Lean to rich( Less than 1.2sec) & from rich to lean (Less than 0.5sec) |
