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07 Black Raven CTS, 07 Gold Mist CTS
453 Posts
DTC PO603 Control Module Long Term Memory Reset

If the battery has been disconnected for any reason DTC PO603 wil set The PCM keeps a running check on the memory, if memory changes it resets. An intermittent loss of power or ground to the PCM will cause a reset.

I have received this DTC several times (it always sets if I have disconnected the battery) and just clear the DTC and see if it returns. Good luck!
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