Nissan dealer repair failed after 350km – advice needed

Need advice on dealing with a failed Nissan repair that's still under warranty.

Timeline:

January: X-Trail started showing idle-stop system errors and engine misfires (RPM surging during acceleration). Nissan Narita diagnosed it as P0300/P0301/P0302 codes (cylinder misfires) and quoted ¥67k for spark plugs + ignition coil replacement.

March 15: Paid ¥69k, they claimed repair was complete. Did NOT provide any post-repair diagnostic report.

March 17 (2 days later, 350km driven): Exact same problem returned. Idle-stop error appeared again, check engine light ON, same RPM issues. I drove 350KM from Narita airport to my city.

Current situation:
Going to Nissan (Aizuwakamatsu – the city I live in) again tonight for diagnosis. I have:

  • Original January quotation showing the misfire codes
  • March invoice showing ¥69k payment
  • Warranty certificate (6 months/10,000km coverage)
  • Photos of the error messages

Questions:

  1. What are my rights here? The repair clearly failed within warranty period.
  2. Should Nissan Narita be responsible for fixing this at no charge, or do I need to pay Nissan (Aizu) and claim reimbursement?
  3. If Nissan (Aizu) finds the parts were never actually replaced (fraud), what's the process for reporting this?
  4. Any tips for dealing with this at the dealership? I have everything documented but want to make sure I handle this correctly.

Has anyone dealt with a similar situation? The fact that they didn't provide a post-repair diagnostic report seems like a red flag to me.

Vehicle: 2014 Nissan X-Trail, 85,700km

by NazgulPhantom