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O.sup.2 -sensor fault diagnosis method and apparatus

  • US 5,685,284 A
  • Filed: 03/14/1996
  • Issued: 11/11/1997
  • Est. Priority Date: 06/08/1995
  • Status: Expired due to Term
First Claim
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1. A fault diagnosis apparatus for an O2 -sensor employed in a fuel supply control system of an internal combustion engine, comprising:

  • an O2 -sensor for detecting concentration of oxygen contained in an exhaust gas of an internal combustion engine;

    feedback control means for controlling a quantity of fuel supplied to said internal combustion engine through feedback control in dependence on an output signal of said O2 -sensor; and

    a microcomputer;

    wherein said microcomputer is preprogrammed to perform;

    a first means comprising an enforcive fuel quantity correcting control circuit for computing if said O2 -sensor exhibits an abnormality on the basis of the output signal state of said O2 -sensor for forcibly changing the amount of said fuel supplied to the engine during said feedback control; and

    a second computation means comprising an input resistance changing circuit for detecting an abnormality of said O2 -sensor in accordance with an abnormality computation process which bears a stronger correlation to the abnormality than the commutation performed by said first computation means, said second computation being performed when said feedback control based on the output of said O2 -sensor is not being performed.

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