C1252 & C1256, brakes in failsafe in cold (<20°) weather

My gen 2 (2004) has started getting a 1252 and 1256 codes, with "brakes" light, buzz, ((!)) light, and "ABS" light when the temp is less that 20 degrees (it is parked outside). It seems to go into brake failsafe mode; it is very hard to brake, because the power brake system is not functioning. When the outside temperature rises, the lights and buzz go away and the power braking functions as it should.

I am suspecting electrical, since I do not hear the booster pump running more than usual (I don't hear it at all) when this occurs.

Ideas? Could someone let me know which relays power the brake booster pump in this model prius?

Thank you for any help!