PDC should beep (even in park) like in the scenario you described once the tranny has been placed in REVERSE. At that point, it's in the "auto" mode and will automatically turn off after a certain distance or speed is reached.

There is automatic activation/deactivation and manual activation/deactivation. If you want it to stop, you can manually deactivate PDC by pressing the button (light should turn off).

Below is the description of how auto & manual activation/deactivation works:

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