<E28> ABS problem

[Pearson-Franks Family <pearsonf@xxxxxxxxxxx>]

Hi, Wes.

Lots of things to suggest.  First, the light is coming on to
indicate a fault mode - the computer is detecting speeds from
the various wheels that do not agree with each other, and it
has taken itself off-line.  If the problem is consistant, it
will be easier to troubleshoot, so let's presume that!  This
fault mode is usually triggered by one (could be more) of the
sensors not developing the correct signal.

I would do one wheel at a time; jacking up the car safely,
removing the road wheel and disk.  Remove the sensor from
the rear of the backing plate; I believe it is secured with a
5mm allen.  If it is crusted with magnetic shavings, sometimes
just cleaning them off will restore operation.  In any
event, inspect and clean the gear-wheel looking thing that
the sensor 'looks at' for its signal.  You will have to remove
the brake disks to do this, so have spare 5mm bolts on hand!
If the teeth of the  sender are crusted with magnetic material,
that will give the symptom.  Before you reassemble, pull the
connector to the sensor apart and inspect for corrosion.
Heck, clean it anyway - tiny wirebrush and spray contact
cleaner, if you stock it.

If you perform this maintenance at all four wheels and the
symptom persists, I would suggest checking the resistance of
each of the sensors as presented at the connector to the ABS
computer itself.  It is above the glovebox, above the ECU for
the fuel injection.  I don't have the ETM right in front of
me (it is out in the garage.  Did I mention it is an _unheated_
garage?) but the resistance of each of the sensors is just
over 1000 ohms.  If any measure drastically different, check
the wiring.  The wires can fatigue internally, especially where
they flex, or the connectors can corrode (but you already checked
for that!).

Hope this helps, Larry F.

ps:  drop me a note if you need the pinout on the connector.  lf

>Date: Fri, 22 Jan 1999 09:34:51 -0500
>From: cwcullen@domain.elided
>Subject: ABS problem-e28
>
>I have an 85 535i with an ABS problem-the ABS light comes on and stays on
>upon reaching about 5mph. From various digest posts I surmmarize the
>problem is probably with one of the sensors. My questions are: Is that
>diagnose correct? Is there any way to test the sensors with a VO meter?
>Are the 4 sensors interchangeable? (buy a new one, and replace one by one
>until find bad one). Are they expensive? Any advice will be appreciated.
>Thanks in advance. Wes Cullen
>
>85 535i
>BMWCCA 138721
>

Larry Franks
Issaquah, Washington
'86 535i x 2
'83 245 GLT (Swedish iron)

------------------------------