Prius (2004-09) :: Code C1365 For ABS / Braking System

Its a 2009 with about 75K miles. Back last year my wife drove through some thick mud, and this caused brake failure....yellow exclamation mark, VSC, and red brake warn lights all on and the buzzer sounding. I did not have mini VCI/ techstream at the time, but I went to car wash and sprayed out the insides of wheels heavily, and then did the jumper trick while pumping brakes 8 times, and the faults cleared and brakes worked perfectly for some months--- until this weekend. We had very heavy rain again, and the tires were encased heavily in mud again. I figured it must be a wheel speed sensor signal problem again. So I took it to car wash to clean inside of wheels.

Now I have the mini-VCI /techstream running on a laptop to check it out. I ran the health check and it came back with code C1365 for the ABS/ braking system. I cleared all DTCs, and the fault lights cleared, but the brakes soon failed again with the same dash indications. Tried once more, same thing. Then I remembered about the trick last year of jumpering the diagnostic connector. This temporarily clears the fault, letting the brakes work fine, until the next time you start the car. Then it comes back. I clicked on that fault code in techstream, and noted that code C1365 was telling me that the accumulator press. sensor voltage was below threshold. Should been at least 4.7 volts, but it was at 4.37.

But the brakes work perfect as long as you don't shut it down! So how can a part really be bad? If it is indeed bad as the code says, is this sensor replaceable by itself, or does the whole accumulator have to be replaced? Is it a job a DIY mechanic can do? I am able to at least drive the car, although my wife can't. I just stick two pins in the diagnostic connector, and I connect them temporarily with a jumper to do the reset trick before each drive.