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2017 CT6 3.6L Rough Idle and Misfire - Help!

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Diana O. · rep 0 · May 22, 3:57 AM · 1 replies · solved · Question

My 2017 Cadillac CT6 Luxury with the 3.6L V6 has developed a really rough idle lately. It feels like it's misfiring, especially when cold, and the check engine light came on. I scanned it with my OBD-II reader and got codes like P0301, P0303, and P0305, indicating misfires on multiple cylinders.

It's got about 70,000 miles on it. The car still drives, but the hesitation and vibration are definitely noticeable, particularly at stop lights. I've been keeping up with oil changes and maintenance.

Any ideas what could be causing this? Could it be spark plugs, ignition coils, or something more serious with the direct injection system? I'm hoping it's not too expensive to fix.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:57 AM

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ClearTheCode guidance (Cadillac · Engine & drivetrain)

Summary: For 2017 CT6 3.6L Rough Idle and Misfire - Help!, 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 Luxury with the 3.6L V6 has developed a really rough idle lately. It feels like it's misfiring, especially when cold, and the check engine light came on. I scanned it with my OBD-II reader and got codes like P0301, P0303, and P0305, indicating misfires on multiple cylinders.

It's got about 70,000 miles on it. The car still drives, but the hesitation and vibration are definite…

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

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