Air Fuel Ratio Imbalance Monitor - Heated Oxygen Sensor (Ho2S) Monitor
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- The air fuel ratio imbalance monitor estimates the cylinder to cylinder air fuel ratio difference using the universal heated oxygen sensor (HO2S) high frequency signal. The high frequency signal is updated at least once per engine combustion event to determine the amount the universal HO2S signal is affected by individual cylinders. The result is a measurement of individual cylinder effect on the universal HO2S.
If the measurement exceeds a calibrated threshold, it is added to a differential signal accumulation window. An accumulation window is at least 50 engine revolutions. The differential signal accumulation is then compared to a calibrated signal threshold. A counter is incremented if the threshold is exceeded. This process is repeated for a calibrated number of total windows. After completing the calibrated number of windows the air fuel ratio imbalance index is calculated. The air fuel ratio imbalance index is a ratio of failed RPM windows over total RPM windows required to complete the monitor. If the air fuel ratio imbalance index exceeds the threshold value the test fails.
- The malfunction indicator lamp (MIL) is activated after a concern is detected on 2 consecutive drive cycles.
Air Fuel Ratio Imbalance Monitor