Some 2018-2019 Fiesta vehicles may exhibit an illuminated MIL with DTC P0128 stored in the powertrain control module (PCM). If the vehicle exhibits this DTC, clear all DTCs and allow the vehicle to sit for a minimum of 3 hours. Then drive the vehicle for at least 16 km (10 miles) and retest for DTCs. If DTC P0128 does not return, do not replace the thermostat valve, release the vehicle at this time. If DTC P0128 returns, refer to the Powertrain Control/Emissions Diagnosis (PC/ED) Manual for normal diagnostics. Engineering is investigating, monitor OASIS for updates.
