The crankshaft variation learn procedure is "required" whenever the crankshaft, crankshaft sensor, block or PCM has been replaced. This allows the PCM to be in very accurate sync with the unique characteristics of the crankshaft to sensor signal. It is for misfire diagnostics. Once a new PCM has had the learn procedure done, the code will not reset. The PCM you are using has had this procedure done already and therefore it is not setting the DTC for the procedure.
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