ABS lamp and beeping - prognosis?

All of the trouble codes have "detecting conditions". Clear them, and you won't see them again until your problem meets the detecting conditions again. That's not the same as the problem going away.

The odd code out in that list is the C1259. All the others are directly related to the braking system. The C1259 is the braking system telling you it got a message from the HV controller about some other problem over there. WIth a scantool capable of talking to the HV and Battery ECUs, you would probably see the additional codes behind that.

But anyway, the detecting conditions for the direct brake-related codes:

C0278: one of two things happened: either the AST terminal voltage deviated from the range 10 to 14 V for 0.2 seconds or more while the SR terminal was below 2 volts, or AST did not deviate from that range for 0.2 seconds or more while SR was in that range. (One infers both signals aren't expected to be simultaneously in that range...)

The INF code you could read with Techstream would tell you which of those two conditions was detected. The workup is 4 pages starting on DI-376.

C1214: You had a difference between the readings of the four pressure sensors, lasting for a second or longer while the brake pedal was pushed. One page of workup on DI-386.

C1251: Either: More than 28 amps flowed to the pump motor for more than a second, or, there was less than a 7 amp change in current drawn while the motor ran, detected more than 3 times in a row. 3 pages of workup starting DI-406.

C1252: Power was supplied to the pump motor for more than 5 minutes. (The fortune cookie for this one is "Pump Motor ON Time Abnormally Long" ... yeah, I'll say! Five minutes??) 7 workup pages starting DI-409.

C1253: List of four possible detecting conditions on page DI-416. The details are there. They are all variations on a pump relay showing ON when expected OFF or vice versa. 5 workup pages.

C1256: Five possible detecting conditions you can find on DI-424. They all involve unexpected signals from the accumulator low-pressure switch (such as it being ON at the same time as the high pressure switch that's one of them). 6 workup pages.

All the page numbers I've given are from a 2001 book, may move around some in other editions.

-Chap