When I first purchased my 1988 M3 the SI lights along the
lower portion of the dash were all fully illuminated. I purchased a
reset tool and followed the procedure but it would not take. I learned
this is the classic symptom of worn out SI Board batteries. These
batteries are intended to save the service indicator memory in case you
disconnect the car's main battery. When the car is running it recharges
the SI board batteries. But over time they lose their ability to hold a
charge and that is when the SI system starts to go haywire. The LED's
will come on and cannot be reset. Eventually your gauges can start to
act funny (tach, temp etc.) At his point it is time to replace the
batteries. BMW did not make this particularly easy, the whole instrument
cluster has to be pulled out to get at the batteries. Some people solder
in a remote connection so that the batteries can be stored farther down above
the pedals. This makes them much easier to access the next time they need
replacing. However, the modern class of batteries is far superior to what
our cars originally came with. The new (NiCad) batteries should last
for quite some time. Below you will find an outline of the procedure that I
followed to replace the SI Board (and the offending batteries).
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