Outline Of Diagnosis: Notes

Detect the slow response of rear oxygen sensor.

Judge NG when the Rich --> Lean response diagnosis or Lean --> Rich response diagnosis is NG and judge OK when both response diagnoses are OK.

[Rich --> Lean diagnosis response]

1. When the measured response time is larger than a threshold, since the A/F ratio is rich, the response time of the output change of O2 sensor when changing from Rich to Lean is measured, and it judges with NG, and when small, it judges with OK.
2. When O2 sensor voltage at the time of a fuel shut-off in deceleration return is large (rich), it judges with NG.

[Lean --> Rich diagnosis response]

1. The response time of output change of O2 sensor when an A/F ratio changes from Lean to Rich is measured, and it is referred to as NG when the measured response time is larger than a threshold.
2. It is referred to as NG when O2 sensor voltage after recovery of fuel shut-off in deceleration is small and still small.