2000 Cadillac Deville P0306 code check engine light on

Hello cadillac70

The cylinder # 6 is misfiring.

The problem ranges from fouled spark plug, broken spark plug wire, broken intake/exhaust valve, to the coil.
Check spark plug in the #6 and it wire, (replace)
Those are easy fix, if the misfire still there after you check or change those; a compression test might be done to determine if it is a broken valve or head gasket.
If there is no problem with the compression, swap the #6 wire on the coil to the one beside it. If the misfire moves to the cylinder that is beside the #6, the problem is with the coil. If the misfire still at #6, the problem should be within the part already mentioned (spark plug wire, broken intake/exhaust valve, head gasket