P0354 OBD-II Trouble Code: Ignition Coil D Primary / Secondary Circuit Malfunction
Trouble code P0354 means there's a problem in ignition coil D circuit, probably an electrical problem, and the engine will run rough or stall.

My wife's 2010 Prius uses the same plugs and I just changed them at 116k miles. It was time. New vs old.Yes I'm aware. It has nothing to do with the cylinder, specifically. It's the ignition pack. The code itself can mean faulty spark plugs, faulty ignition coil, vacuum leak, air control valve malfunction, etc. I was just assuming that since I never took out the coil, cylinder 4/D would have ignition coil D relayed to the PCM via the factory wiring
I am planning to swap the "cylinder D" iginition coil with "cylinder C" and see whether I get a Ignition C malfunctions. But another member told me to take both the spark plug and coil out and look for blue or orange color at the arc of the plug