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Plausibility criteria

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The following criteria are important for checking the plausibility of air ratios:

  1. When in a steady state, the air ratios upstream and downstream of the oxidation catalytic converter are virtually identical.
  2. The air ratios fluctuate within the ranges shown in the examples.
  3. The signal from the oxygen sensor downstream of the oxidation catalytic converter follows the signal from the upstream oxygen sensor after a certain time delay (approximately one second).
  4. Erratic changes to the air ratio are signalled virtually immediately by the oxygen sensors.
    NOTE: Heavy fouling of the upstream oxygen sensor can mean that its signals are delayed by up to two seconds. In this situation, the signal from the oxygen sensor upstream of the oxidation catalytic converter is sent after  the signal from the downstream oxygen sensor.
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