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From digest.v7.n379 Sat Oct 4 16:13:31 1997
From: Otter <kdsebe0_at_pop.uky.edu>
Date: Sat, 4 Oct 1997 15:16:48 -0400 (EDT)
Subject: ABS analysis, rather longish
Okay, since I got a large number of requests on what the dianosis of my
system on my 1986 325 was, I've decided to write down what my mechanic
and I looked for.
- Check the ABS sensors. The wheel sensors are essentially voltage
generators, as the spinning magnet produces a current, and thus a voltage
(remember Ampere's law?). Starting with the rear sensors, pull up the
rear seat to access the connectors. Beneath the felt cloth, you will find
a connector at each rear corner. On my car, the connector was a round
beigeish connector about 3/8-1/2" in diameter, as I recall. The connector
simply has two prongs on the sensor side. Attatch a voltage sensor (read,
digital multi-meter) and spin the wheel (did I mention that you want the
wheels in the air at this time?). Do this for both rear wheels. If you
get no voltage reading, than you have a bad sensor. Then try the front
wheels. On my car, the front left was located on a clip to the left of
the shock tower. I don't remember where the front right was, as my
mechanic did that one, but I believe it is located further down to the
left of the right shock tower.
- However, none of this worked. Time to start trying relays, as that is
really all that is left in the system to go wrong. Unscrew the top of the
ABS unit (there is one screw in the center that holds it on) and you will
find a few relays located underneath this black plastic cover. If you
don't know what your ABS unit looks like, it has _lots_ of metal brake
tubing coming out of it and should be located in the front left of the
engine compartment.
If none of these relays are the problem, than there is one more relay
that I know of, located under the steering wheel. Take off the underdash
cover and look above a flat metal box. There should be a silver relay
clipped above the box. It is a bit of a hassle to get to, but you
shouldn't need to take anything out. Finding it is much harder than
removing or installing it. I would suggest a flashlight around now. This
relay calls $42.50 at the dealer, which we all know is absolute rape. But
the dealer does guarantee the parts, and you _do_not_ want a used part
which might have already failed.
3) Something I read about on the net concerns the instrument cluster
lightbulb for the ABS system. This IS part of an ABS relay system, basically a
fuse, so if this lightbulb doesn't briefly light when you start the car,
your bulb is burnt and must be replaced for the ABS to work.
4) Last thing I know that can go wrong is the pump. I don't know how to
test this, but my mechaninc assured me that if the pump fails, you will
have a catastrophic failure in the brake system. Ie, pedal goes *all* the
way to the floor. Then would be a good time for an E-brake manuever.
Pumps are very expensive, but fortunately, you will know if you need one
or not =)
Hope this helps whoever has ABS problems with their E30. This may even be
suitable FAQ material, as I found a large dearth of information on this
conundrum.
Kenn(y)(eth) Sebesta
1986 325
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