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2018 CT6 3.0TT Rough Idle and Misfire - Check Engine Light On

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Eric V. · rep 0 · May 22, 3:59 AM · 1 replies · solved · Question

Vehicle: 2018 Cadillac CT6 Platinum

Hey everyone,

My 2018 Cadillac CT6 Platinum with the 3.0L Twin-Turbo V6 has developed a really rough idle lately. It feels like the engine is shaking more than usual, especially when I'm stopped at a light. The check engine light came on a few days ago, and it's been pretty consistent.

I took it to AutoZone for a quick scan, and it pulled a P0302 code, indicating a misfire on cylinder 2. I'm wondering if this is a common issue with these engines or if it's something simple I can check myself before taking it to the dealership. Any advice on what to look for?

It's got about 65,000 miles on it, and I've kept up with all the regular maintenance.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:59 AM

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ClearTheCode admin answer:

A P0302 code indicates a misfire detected in cylinder 2. This is a common diagnostic trouble code that can stem from several issues in the engine's ignition, fuel, or compression systems. Given your vehicle's mileage, several components could be nearing the end of their service life.

Common Causes:

  1. Faulty Spark Plug: A worn or fouled spark plug in cylinder 2 is a very common cause of misfires.
  2. Defective Ignition Coil: The ignition coil for cylinder 2 might be failing, preventing a strong spark.
  3. Clogged or Failing Fuel Injector: An injector that isn't delivering enough fuel, or is stuck open/closed, can cause a misfire.
  4. Vacuum Leaks: Leaks in the intake manifold or vacuum lines can lean out the air-fuel mixture, leading to misfires.
  5. Low Compression: Less common, but internal engine issues like worn piston rings or valve problems can cause low compression in a cylinder.

Troubleshooting Steps:

  1. Check Spark Plug & Coil: If you're comfortable, you can inspect the spark plug and ignition coil for cylinder 2. Sometimes, swapping the coil with an adjacent cylinder (e.g., cylinder 4) and seeing if the misfire code moves (e.g., to P0304) can help diagnose a bad coil.
  2. Fuel System Cleaner: Try a high-quality fuel system cleaner, which might help if the injector is slightly clogged.
  3. Visual Inspection: Look for any obvious loose hoses or wiring around the engine.

When to See a Shop: If the misfire persists after basic checks, or if you're not comfortable performing the above steps, it's crucial to take your CT6 to a qualified mechanic or Cadillac dealership. Ignoring a persistent misfire can lead to more severe damage, such as catalytic converter failure due to unburnt fuel entering the exhaust system. A professional can perform more in-depth diagnostics, including fuel pressure tests, compression tests, and advanced scanner diagnostics to pinpoint the exact cause.

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