{HEAD ~ A diagnostic apparatus} applied to internal combustion engine exhaust gas sensors employing electrochemical polarographic principles indicates {TAIL ~ sensor operation} relative to a current limiting operating region in which a sensor output signal indicates oxygen concentration in the exhaust gas 
indicates
{ HEAD ~ A diagnostic apparatus } applied to internal combustion engine exhaust gas sensors employing electrochemical polarographic principles indicates { TAIL ~ sensor operation } relative to a current limiting operating region in which a sensor output signal indicates oxygen concentration in the exhaust gas
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