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Air/fuel ratio control diagnostic

  • US 5,656,765 A
  • Filed: 06/28/1995
  • Issued: 08/12/1997
  • Est. Priority Date: 06/28/1995
  • Status: Expired due to Term
First Claim
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1. An air/fuel ratio control diagnostic method for diagnosing the performance of an automotive internal combustion engine air/fuel ratio control system in maintaining engine air/fuel ratio within an air/fuel range corresponding to efficient catalytic treatment of engine exhaust gas by a catalytic converter, comprising the steps of:

  • providing a signal indicating oxygen concentration of engine exhaust gas that has been treated by the catalytic converter;

    defining an oxygen concentration signal range for the provided signal extending between a predetermined upper and a predetermined lower oxygen content signal threshold, and corresponding to efficient catalytic treatment of the exhaust gas;

    initiating a test period;

    periodically sampling the provided signal during the test period;

    comparing the signal samples to the defined signal range to determine if any signal excursions outside the range occur;

    estimating a duration of any signal excursions outside the defined signal range;

    comparing the estimated duration of any signal excursions to a threshold duration; and

    indicating deteriorated air/fuel ratio control system performance if the estimated duration of any signal excursion exceeds the threshold duration.

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