ABS pressure switch gone South

In November 2009 my ABS light started to blink. Retrieving the error code with Espritmon yielded error 62, low accumulator (see picture below).



Using Espritmon I plotted the pump run time and the brake actions.


The red lines indicate when the brake is pushed, and the black ones when the pump runs. As can be seen, every time the brake was pushed the pump would run, indicating that either:



For comparison purposes, the following plot shows the pump run and braking actions a couple of months earlier:


Here, the pump would run only every four braking actions.


I didnít immediately have a replacement switch but kept recording the brake and pump actions for the next weeks. The ABS light blinks, but at this moment the only problem is that the pump runs more frequently. However, since it still only runs after you press the brake pedal the total amount of time the pump is running is not really worrisome in terms of wear.

However, the problem got worse rather quick (matter of weeks). At some point the pressure switch would continuously provide pulses to the pump relay, also with the brake not being pressed (see the right bottom plot in the picture below)! Also, when pressing the brake pedal, the pressure would drop below 1800 psi causing the brake tell tale to become active. At this point I really needed a new pressure switch!



About 260 samples later, the pressure switch indicated low pressure (see picture below)


And right after that (10 frames later), the system generated error 36, No Pump, see picture below.



A friend donated his spare ABS unit from which I used the pressure switch (grey one in the picture below) and now everything works perfect again. Thanks Peter!


Unit with pump, accumulator and pressure switch


The infamous pressure switch, basically unobtanium


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