Some engines had cylinder head problems, usually noted before 15K. The number one cylinder valve guides would wear abnormally. The repair is to replace the cylinder head. Before March of this year, the replacement head was the same as the old one, so the condition could occur again.
After March of this year, the head released for service, or installed on the engine at the plant, has hardened valve guides which solves the problem.
Root cause analysis has not determined exactly why some wear, some don't. Warranty is still not that high on the I-5 or the I-4 engine (same head design).
Symptoms are a rough idle and code P0300+, which are misfire codes due to the valve guide wear. If it fails, it will fail under warranty; unless you only put on about 2K miles a year.
A new repair procedure has been developed that drops the time to replace the cylinder head from 18 hours to 8 hours (no thanks required, it was part of the job
). Old procedure required the oil pan to be removed to remove the front cover, new procedure does not even require front cover removal.