Check hybrid system light in and just had it services!

If the car is under warranty, I’d recommend returning to the dealer. They need to find and fix the leak; drain, fill, and bleed the air out of the inverter cooling system; and then confirm that there isn’t another problem and that nothing has been damaged from the lack of proper cooling.

The “inverter fluid” is the coolant for the inverter with converter assembly (the power control unit for the hybrid system) and the hybrid vehicle transaxle. It’s the same kind of pink, Toyota Super Long Life Coolant (SLLC) used in the engine cooling system, but the inverter cooling system is separate, with its own water pump, reservoir (Owner’s Manual (PDF), page 612), and piping. If the coolant level has gone from full to low in a week, there is a leak somewhere; it’s a closed system, so coolant shouldn’t just disappear, but because of the plastic covers under the engine compartment, you might not notice anything dripping or leaking under the car.

If the dealer can’t find the leak just by looking for it, they need to use a radiator cap tester to do a pressure test of the inverter cooling system. The Repair Manual (more info) includes a step-by-step procedure for this.

When “Check Hybrid System” appears, diagnostic trouble codes (DTCs) are stored in the car’s computers, from which they can be retrieved using a Toyota Techstream diagnostic system, available at all dealers. The Repair Manual explains the likely causes and troubleshooting procedures for each DTC. Ask the dealer to tell you the stored DTCs, or better yet, give you a printed “Health Check” report from the Techstream software.

 

The signature says "2010 Prius" and I wonder if the "2019" in the post was just a typo. The "9" is next to the "0" after all.