Reduced Braking Power - Brakes Completely Dissappear

[AliceMcG87]

Hi all. I'm hoping for a bit of urgent help as my car almost killed me on a steep hill
My 2004 E220 has suddenly developed a beaking issue. It gies from all fine and dandy to no brakes with 2 sometimes 3 malfunctions. All pressure on the braking peddle dissapears completely and I get the warning 'Reduced Braking Power, Start Engine!'. Which is a bit on an understatement when the brakes have vanished.....
The main battery had been very weak and seemed to increasing the malfunctions, a quick test with the amp meter showed it was dead.
Put a new (slightly more powerful) battery on this afternoon and drove about my estate with no issues. But when I went to leave the estate (off a steep hill) an hour later the issue suddenly reappeared without warning.

Can anyone offer any helpful advice pls?
My local mechanic can't read it and the nearest AMG is a good few miles away, plus we eould rather be able to fix it ourself (we're not complete mechanically unsavvy)

Thanks

 

[AliceMcG87]

Update. After giving the SBC bush a bit of a tap, the warning instantly disappeared

 

[LostKiwi]

It's a possible indication the SBC pump needs new brushes in the motor.

At 73k miles it's quite early for SBC issues but not unheard of. Do you use it a lot around town?

 

[AliceMcG87]

Hi @LostKiwi
Yes, its mostly town driving

 

[LostKiwi]

Ok that probably explains it. It may be worth budgeting for an SBC pump refurb (around £500) sometime soonish. You may be lucky and find it's a one off but it could be an early warning.

SBC uses the pump to provide high pressure to the brakes. The pedal them modulates the pressure in the system and applies it to the brakes. Over time the motor brushes wear. There is also a counter that will warn (with a similar warning in white) when the system is getting near its expected failure time (usually about 100k miles). The counter works in the number of brake applications hence town use sees it fail earlier, motorway use later.