This bulletin applies to 2017 Kia Optima hybrid/Optima plug-in hybrid vehicles.
You may see a “fill inverter coolant” message on the cluster after performing an HEV system service requiring the coolant to be drained. The logic for this message is such that it will be displayed when the RPM of the EPW (electric water pump) climbs while the load goes down, indicating a possible cavitation. This is due to air in the system.
Much like bleeding any fluid system utilizing a pump, the hybrid cooling system must be bled in a particular manner to avoid aeration.
To accomplish this, you would first follow the instructions in KGIS shop manual section>Hybrid Motor System>Hybrid Motor Cooling System>Coolant>Repair procedures. If the message is still displayed after completing the procedure, cycle the pump with KDS, on for five seconds, and off for five seconds, ten times. Let it settle for one minute, then repeat the on/off cycle five more times.
Check that the water level is located between high and low in the inverter coolant reservoir.
There should be no air bubbles in the coolant. If air bubbles are found, retry the EWP actuation after 30 seconds.
