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Brake warning light

colinb1

colinb1

New member
Hi - I've just gone to start my 1990 Carrera 4 (LHD) and find that the brake warning light is on and the pedal pushes easily to the floor. It gets stiffer after being pressed several times but the warning light stays on.
When I drove it last on Sunday (4 days ago) - it was fine. Any ideas please?

thanks
Colin
 
Hi - thanks for the fast reply. I have checked that and when I unscrewed the cap, there was fluid visible directly underneath.
When the engine is not on, I can pump the pedal up to what feels like 'normal'. As soon as I turn the engine on it sinks under pressure again.
There are no leaks visible either in or around the reservoir.

Colin
 
Colin,

The C4 uses a high pressure braking system which is driven by an electric pump. Can you hear that pump running (in the luggage compartment) when you turn the ignition on before starting the engine?? It should stop after a minute or less once sufficient pressure has been built up. A few presses on the brake pedal should bring the pump back into action.

Let us know the outcome and we can progress further.

Regards

Dave
 
Dave - thanks for that suggestion.
I'll take a listen in the morning. Where is the pump? Is it near the battery at the front? The reason I ask is that right next to the positive battery terminal is a unit of some description and it is so close to the terminal it is almost touching - not sure what it is though.

Colin
 
Colin,

Yes, it's very near the battery. The pump generates a HUGE pressure - something like 260 bar - and there is a pressure vessel (like a small globe) which retains the pressure. The pump has a pressure limit switch attached to it (it's green) which has been known to fail. If this happens the pump fails to switch off and is in grave danger of self destructing if it runs for much more than 2 minutes. It can get VERY hot and will melt some of the pipework and will eventually leak brake fluid into the luggage compartment. The pump is VERY expensive to replace although the switch and pressure vessel less so.

Before you start looking for other possible problems it's crucial that you confirm that the pump operates correctly and switches off (and back on).

IIRC failure of the hydraulic pump usually results in a very hard brake pedal - not soft as you describe. So it may be that the problem is elsewhere.

Regards

Dave

BTW Colin, it might be useful if you could confirm WHICH light(s) come on. Do you get the gong at any time??
 
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