This bulletin applies to 2017 Kia Optima Hybrid vehicles. Some technicians may report seeing the “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 EWP climbs while line 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 this message is still displayed after completing the procedure, cycle the pump with KDS, on for five seconds and off for 5 seconds, 10 times. Let it settle for one minute, then repeat the on/off cycle 5 more times.

Allow the coolant to settle for another minute. Then run the pump the full run time of 90 seconds and listen to the pump. You will hear a gurgling/sloshing sound if air is still present. 

If no sound is heard and you verify that no bubbles are present, bleeding is complete and the message should no longer be present.

Check that coolant level is located between High and Low in the inverter coolant reservoir. There should be no air bubbles. If bubbles are found, re-try the EWP actuator after 30 seconds.

Check that coolant level is located between High and Low in the inverter coolant reservoir. There should be no air bubbles. If bubbles are found, re-try the EWP actuator after 30 seconds.

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