My very cheap $4.35 Chinese OBDII unit can sometimes cause various Prius warning lights, including the red triangle, to come on unexpectedly without any fault code been logged. Unplugging the OBDII unit resolves the issue.
I actually discovered I had the very same issue on a 2010 Prius 3 with 100.000 kms Cheap OBD2/BT adapter from amazon. Torque pro app on android. The problem happened 3 times in 2 days. My dealer has analyzed the issue without the OBD adapter and found nothing but a weird fault code in the memory of the car. Now I drove about 50 km without the adapter without any issue then I put the adapter back and I had the issue very quick after stopping the restarting the car with torque app on.
