According to a Toyota press release, the problem is due to some potentially faulty transistors on a circuit board in the SUV's inverter. The transistors may have been poorly soldered onto the circuit board, making them more susceptible to heat produced during operation.
The recall affects 45,500 Toyota Highlander Hybrid SUVs and 36,700 Lexus RX 400h SUVs that were sold in the US. The suspected problem only applies to 2006 and 2007 model year vehicles, and Toyota says that no other Toyota or Lexus vehicles are affected.
In a worst-case scenario, the hybrid system could fail completely, causing the vehicle to coast to a stop. During a more common type of failure, the SUV would enter a fail-safe driving mode that allows it to continue driving for short distances.
According to Toyota, heavy loads or hard driving will increase the heat in the system and make the SUV's electronics more prone to failure. Any issues related to the recall will likely be accompanied by a loss of power and various warning lights turning on in the instrument panel.
Starting next month, Toyota will be sending letters to Highlander Hybrid and RX 400h owners with more information. The Japanese automaker is currently stockpiling all the parts needed to make the repairs.
Once all of the necessary materials have been collected, Toyota will send out a second notification to owners recommending them to contact a local dealer and set up an appointment for repairs. The dealers will be able to check the SUV's electronics and replace any faulty electronics found free of charge.