According to Toyota the Intelligent Power Module (IPM) located inside the Hybrid System Inverter contains a control board with transistors. Certain transistors on the control boards in some of the subject vehicles were inadequately soldered and could be damaged from heat caused by a large current flow during high-load driving. If this were to occur the worst thing that could happen is that the power supply circuit fuse could blow and the hybrid will coast to a stop.
Toyota is currently obtaining the necessary replacement parts and will notify owners in mid July.
The recall affects approximately 45,500 Highlander Hybrid and 36,700 Lexus RX 400h vehicles.