So I am wondering.... for my '94 XJS with brake problems, how do I tell that it is a faulty accumulator or a leak somewhere else in the system? Leaving the car for a few hours (or depressurising it by pumping the peddle while it is off) means that the little electric pump runs for about 10 seconds to fill up the accumulator and turn off the lights. I can tell by the voltage signal that every time I press the brake pedal the pump runs. Is this 100% a blown accumulator or could it be that I have a leak somewhere?

 

From what I experienced, if the accumulator has not been replaced, it is now 20 years old on your car. It is a normal service item, far beyond its service life. Second, when you turn on the switch, allow the accumulator to build up, turn the switch off. Depress the brakes. If the pedal goes hard pretty quick, like 6-10 pumps, accumulator is shot. Made a big difference on my 89, as I feel it had never been changed.

 

OK thanks. I'll see how that goes.

 

I would also agree that you should go ahead and replace it, although some of those signs aren't necessarily condemning. If you can tell by voltage that the pump come on whenever you use the brakes, I would think that is normal, as it always wants the accumulator topped up. If you mean your light comes on for low pressure, then that is different.

As for it taking a long time for the light to go off, there may be air in the system, causing it to take longer to reach the correct pressure for the light to go off.