Re: bmw-digest V5 #237

Subject: Re: bmw-digest V5 #237
From: Desmond Stagg <Desmond.Stagg@domain.elided>
Date: Mon, 16 Sep 1996 12:46:20 -0700
Matthew Hocker wrote:
>
From: Matthew Hocker <hocker@domain.elided>
Date: Sun, 15 Sep 96 22:35:58 -0400
Subject: <E30> ABS failure... again

Well, the ABS on my 325iC failed again. I was driving on a highway and
just  
happened to glace down and see the "orange light of doom" illuminated on
my  
console. I powered off the car at the next stoplight, resetting the
light, but  
as soon as I started moving, it came on again.

Grrrr... I've had the system fail before.

Before, it was a witch hunt, but with a relatively simple solution. All
I had  
to do then was replace the fusable relay and the dash bulb. Check my
web  
page, I was actually pretty impressed with myself back then. The system
then  
worked fine (and for about a year). Until today.

So, later this evening, I started looking at the sensors. I looked at
both  
the front ones, they looked ok (although I didn't have a jack, so it
wasn't  
very easy to turn the wheels and check that all the teeth were ok) but
I  
couldn't find the rear ones. I sprayed some WD-40 on the front ones to
see if  
it would help (it didn't).

According to the documentation I have (not Bosch docs) there should be
rear  
sensors, but from what I can see, there don't appear to be any. Bentley
says  
(in the pathetic paragraph that is their ABS coverage) that there is a
single  
sensor in the rear differential. I can't find it. Can anyone give me a
clue  
here?

Now, obviously my visual abilities are not satisfactory to diagnose
this  
problem. How can I electronically (or otherwise) analyse this system?
Some  
documentation I have talks about a Bosch "T" connector for doing work.
Is this  
a ludicrously expensive part? Can I build one of my own?

Any help from those in the know about ABS would be MOST appreciated.

Cheers,
>

With reference to the above problem: 

I dont know if this is applicable in your case, but having different
size tyres front and rear will cause the ABS light to illuminate.

This was a problem many M3 drivers had after fitting larger wheels to
the rears only. As you drive off the ABS computer checks the logic of
the system, and if the signals from the front and rear wheels do not
coincide then for the computer this is not logical thus causing the ABS
light to illuminate.

Other than that I cannot offer an instant solution unless one sees the
car.

Regards

Desmond Stagg
mailto: Desmond.Stagg@domain.elided