Elantra Hybrid High Voltage Error

I own an Elantra Hybrid and had a similar issue. The "high-voltage system error" sounds like your car's ECU is detecting a fault in the hybrid system. These systems run at much higher voltages, which is why that error appears. The engine shutting off and reduced power sounds like a safety measure by the ECU to prevent damage. Have you noticed any battery drain issues?

Battery drain issues? I hadn't specifically noticed, but the car has been sitting idle a bit more than usual lately. Could a heavily discharged battery cause such problems with the high-voltage system?

Yes, a heavily discharged or defective high-voltage battery can cause those symptoms. When the voltage drops too low, the inverter might not function correctly, leading to system malfunctions and error codes. The ECU protects the hybrid system, so that explains the engine shutting off and reduced power. I took mine to a workshop. They scanned the system, found a fault, and replaced a cable. I suggest you do the same.

Your insights have been invaluable! I took it to my local mechanic, and they confirmed a faulty cable within the high-voltage system. The repair cost 290€. Thank you so much for your help!