NHTSA Complaint #11699689 — 2018 HYUNDAI ELANTRA

Initial Fault Code: P0303 Replaced all 4 spark plugs and all 4 ignition coils. The check engine light extinguished momentarily but returned, logging P0303 and a new P0301 Replaced all 4 fuel injectors. CEL extinguished momentarily and then returned, logging P0303. Replaced the entire engine electrical harness. Concurrently, all related electrical components and connectors were meticulously cleaned with professional contact cleaner. CEL extinguished for significantly longer period of time, and then returned, re-logging P0303 and P0301. Thid suggested the ECU was "handshaking" with new components but re-logging the fault upon detecting the persistent core issue. A full compression test was performed. All cylinders reported results within specification. Using a borescope I inspected cylinder walls in piston tops. There was significant carbon residue buildup but nothing out of the ordinary for similar GDI engines. I still performed a PEA GDI specific chemical cleaning. It was a a little smoother afterwards, but the misfire persisted and CEL remained on. I also removed, cleaned, and tested common sensor faults, with no result. Also p0128 code and no start / electrical drain, and engine light started flashing numerous occasions had to stop the vehicle. I tried swapping the coils, but all that proved was that the coil was good, I did a power and ground test, it passed the connector had 12 plus volt power and a perfect resistance to static ground. The signal wire from the coil connector had perfect continuity to the ECU but had OL to chassis ground showing there was no short. A test light was used to see if anything was coming from the signal wire to the ignition coil and that test failed, there was no signal pulse. The diagnostic process has definitively proven a component-level failure inside the engine control unit. See attached file for more detailed information.