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From digest.v7.n379 Sat Oct 4 16:13:31 1997
From: Otter <>
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.

  1. 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.
  2. 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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