This Preliminary information communicates to the dealer technician that if they are unable to perform the solenoid characterization using the transmission unit number (TUN) off a replacement 8L90 RPO M5U automatic transmission to refer to the TUNs listed in this PI. If the TUN off the replacement transmission is listed they should refer to bulletin 18-NA-355 and perform a transmission fluid exchange due to possible fluid contamination. The dealer technician is to call technical assistance after the fluid exchange to get the TUN unlocked so they will then be able to  complete solenoid valve characterization procedure.
