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:
- The ABS accumulator lacked
pre-pressure or
- The ABS pressure switch senses
the high pressure where it should turn the pump off to early (at a lower
pressure than 2700 psi).
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 didn’t
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