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FaultDetection counters from the standard

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Full Member level 5
May 4, 2012
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I found the following from the standard

  • FaultDetectionCounter1 -> The maximum value that FaultdetectionCounter0 has reached during the current operation cycle.
  • FaultDetectionCounter2 -> The maximum value which is equal to greater than unconfirmedDTCLimit, that the FaultdetectionCounter0 has reached since the last time DTC information was cleared.

The first one looks little easy. But the second one is little complicated to understand. Please help me to understand. Let us say the unconfirmedDTCLimit is some 10.
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The Fault detection counter is a variable used for test pass or fail of a component. If a test fails the counter will increment by say 10 and if it passes it decrements by 1. If the counter reaches certain maximum value(127) the component is assumed failed and if it reaches fixed minimum values (-128) then the component is passed. This is used for logging Diagnostic Trouble Codes (DTC). So, my question was that the second line was little confusing.


  • Diagnostic-concept-in-the-vehicle_593757.pdf
    68.2 KB · Views: 209

Regardless of the application of this, the algorithm you describe later (and only now the question makes some sense), it seems that on the computation of the shift average it is assigned a larger weight to the failure than to the normal operation, so that after the occurrence of few events of fails the threshold to trigger the alarm is reached, whereas to pass the test, it is necessary to have a much greater number of successful events to cancel the effect of the failures.

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