2017 CT6 V6 Misfire - P0304 Code and Rough Idle

ClearTheCode guidance (Cadillac · Diagnostics & codes)

Summary: For 2017 CT6 V6 Misfire - P0304 Code and Rough Idle, work through these steps on your 2016+ vehicle:

1. Confirm the symptom — note when it happens (cold start, highway, after fuel fill, etc.).
2. Scan codes — save all pending/stored DTCs; don't clear until you've recorded them.
3. Check TSBs & recalls — look up your VIN for open campaigns and known fixes.
4. Inspect the obvious — related fuses, connectors, fluid level, and recent repairs.
5. Test the common fix — follow model-specific service procedures; one change at a time.
6. Escalate if needed — burning smell, no brakes, overheating, or stalling in traffic → shop visit.

Owner reported: My 2017 Cadillac CT6, 3.6L V6 Luxury trim, recently started running really rough, especially at idle. The check engine light came on, and when I scanned it, I got a P0304 code, indicating a misfire on cylinder 4.

I've noticed a slight decrease in fuel economy too. It feels like it's struggling a bit under acceleration, and there's a noticeable vibration.

What could be causing this? Is it likely …

This is educational guidance, not a substitute for hands-on diagnosis.