This is one of those messages that Volvo decided to confuse and worry everyone with, isn’t it? You see it come up, when the alert buzzer sounds, and you think, “Oh, s**t!!”, and with 50-60 passengers on board, you’re right to! It’s not as bad as it seems. The B7RLE is *almost* 100% computer controlled, including the air system, brakes, air conditioning, fuel & air intake, air compressor & discharge system, and faults are common, but they’re mostly friendly warnings that a serviceable part is nearing the end of its life, but these “friendly” messages were written to scare you, it seems, and sometimes, rightly so, in the case of First Manchester, who ignore service warnings completely, and run the bus until something fatal goes wrong, then scrap the bus.
For this error, it is mostly the brake disc and/or pad sensors detecting that the pads/discs are nearing their safe limits. Connecting the Volvo software up to the bus computer will verify this. The brakes aren’t going to give in. If they were, the emergency stop system would kick in, and bring the bus to a safe halt, and shut off the engine and fuel system.
Clear the ECU log after correcting the cause, and the warning will go away. I usually clear both the main bus ECU and the brake ECU at the same time, to clear the air, between the two, so to speak.