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Oxygen heater sensor diagnostic routine

  • US 5,392,643 A
  • Filed: 11/22/1993
  • Issued: 02/28/1995
  • Est. Priority Date: 11/22/1993
  • Status: Expired due to Term
First Claim
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1. An oxygen sensor heater diagnostic method for diagnosing the condition of an oxygen sensor having a heater and located to intercept the exhaust gases from an engine, comprising the steps of:

  • shutting off the heater;

    preventing the exhaust gas of the engine from heating the oxygen sensor;

    measuring a first output voltage of the sensor at a sensor output as a value V1 when connected to a supply voltage through a large pull-up resistor;

    measuring a second output voltage of the sensor at a sensor output as a value V2 when connected to a first predetermined voltage through a small pull-up resistor;

    determining an initial delta reference voltage by subtracting V1 from V2;

    using said initial delta reference voltage to indicate the sensor internal resistance as of the measurements; and

    monitoring the magnitude of the initial delta reference voltage.

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