Thanks for the reply.
I'm trying to figure out how these readings are possible because: a) fluid level is definitely not low b) parking brake is definitely not ON (I hardly ever use it, but just went out and checked it, anyhow)
So I'm almost certain that "P" is false, and that casts some doubt on "!", too, although because of the other possibilities, I can't rule out anything yet.
I think for now I'll assume that this is an electrical problem and check out wiring and sensors individually before anything else.
Where are the fluid level sensor and the pressure differential switch? Somewhere in or around the master cylinder?
TIA