[jimk]

Heads up to the owners of MY 2018 M550i. Chances are that you will experience a fault (P0128) with the CEL illuminated which is related to a bad thermostat. There’s a BMW warranty that extends the thermostat warranty to 15 years/ 150,000 miles. The coolant is leaking from the thermostat and can get into the electrical connector and harness causing a major damage. Luckily, mine was fine. The screenshots below are from the video inspection. Hopefully this is useful.

[430Scud]

There are three specific extended warranty items for 2018 M550iX.
Thermostat
Intercooler
Radiator flaps/shutters

All are warranted for 15 years or 150,000 miles

Attached is the thermostat SIB