p0621 code,headlamps flicker at idle,altenator is 14.60v ok,car starts and runs ok.
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2004 Pontiac Grand Am
Answer #1ProChevy August 17, 2009, 10:50Journeyman
This code is a high alternator turn-on signal circuit voltage code which means the Powertrain Control Module is detecting a high turn-on voltage at times. Possible causes could be the alternator or the PCM more than likely. The car will need to be checked by someone with a scan tool to monitor this circuit to see if the fault is constant or intermittent. Hope this helps.