2014 rcz with 48k on the clock, first went into limp mode with engine problem message. Got a code reader which showed misfire on cylinder 4. Changed plugs and coils but problem still remained. Went into Peugeot dealer who ran a compression test on cylinders and found practically zero compression on cylinder 4. All others are fine 150psi. They say the next step is to remove the head and investigate but if it turns out to be carbon build up it won’t be covered by extended warranty. I had no warning, ie steady loss of power, just this sudden failure. Is it likely to be carbon build up?