DON'T PANIC YET! About 700 miles ago my 2013 Prius dash lit up like a Christmas tree! My OBD2 reader showed a c1391 code that a dealer said would cost around $2500 to repair! But, braking was OK, pump ran normally, regen OK and no fluid leaks although the level was down a little bit. A local mechanic confirmed the code and took it for a ride. When he came back he said the code was cleared! He said he did that by slamming on the brakes at about 25 mph! Well, the code came back, but I was once again able to clear it by brake slamming. Obviously something strange was going on. Using the somewhat lowered fluid level as a clue I checked the brake pads. The front pads were relatively new, but the rear pads looked like they had about 50% wear (near 100k miles), so I replaced them and adjusted the fluid level. I took it for a ride and did the brake slam again and the lights ultimately cleared. A code check a few days later confirmed that the c1391 code was gone. 700+ miles later and all is still good.
