P0306 code

[m3reno]

My friend has a 2020 wrangler with the 3.6 non e-torque with 29,000 miles. Today at first start the vehicle started but about a minute later it started to run rough for about 15 seconds then threw two CEL lights one being the start stop and the second is the yellow engine icon (code P0306). The Jeep rides perfect but I was concerned because I know any type of 300 codes are usually bad. He has a appointment with the dealership next week but i was wondering what steps should the dealership be taking for this code. Thanks

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[alphawolff]

Misfire on cylinder #6. General misfire diagnostics is to swap the coil and plug to adjacent cylinders to see if the misfire chases one of the components. If issue remains the injector is typically swapped along with a leak down test to verify cylinder head seal integrity.

29k is low mileage for a head gasket, and if it was a cylinder head issue it wouldn't just start misfiring randomly after about a minute. It'd be misfiring immediately upon start. This indicates the issue begins occurring with increasing engine temperature. My bet is a defective coil, plug, or injector. It's probably the coil.

If the misfire happened once then didn't return that will throw a wrench in the diagnostic strategy. The dealership will verify the misfire is currently happening before going down the diagnostic path. #6 is located under the intake manifold, so diagnostic could prove a bit more involved. Do not be surprised if they quote your friend ~2 hours of labor to begin tearing it apart.

 

[m3reno]

Wow Thanks for the quick reply!

 

[tk1700]

alphawolf has some great info! I had the same codes at about 51k miles on a 2019 3.6. Ended up with a new engine due to blown head gasket and scored cylinder. Good luck to your friend.

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