[No EFI] ABS Help Needed

[Malcolm Robb, LC 0112G]

Here in Euroland, most GM/Vauxhall/Opel cars use Bosch ECU, ABS, Gearbox, 
Digital Dash, Trip Computer etc. The Tech1 scan tool can be used to 
diagnose all of these units, and read out fault codes. I do have a list of 
ABS fault codes somewhere, so if your unit is a Bosch one, then perhaps I 
can help. Unfortunatley, the wiring to allow the diagnosis was only added 
to cars here post '94, so for cars before that year, you have to remove the 
unit from the car, which rather defeats the purpose of the scan tool !

If you haven't got access to a Tech 1, then I believe it is possible to get 
the fault codes to flash up on the ABS light in the same way as you can get 
the ECU to flash up Trouble codes on the CEL lamp.

Since this is an off topic request, EMAIL me off list if you are 
interested, and I'll forward what I have. But almost all the ABS faults 
that people have here are due to worn suspension rubber bushes, which allow 
the rear axle to move slightly, which takes the sensor out of range of the 
castellated drive shaft rotor thingy, and the ABS unit then flags a fault.

Cheers,
Malcolm Robb, LC 0112G

-----Original Message-----
From:	Rich Vandervoort [SMTP:richvandervoort at hotmail.com]
Sent:	Tuesday, May 02, 2000 12:53 AM
To:	gmecm at diy-efi.org
Subject:	Re: [No EFI] ABS Help Needed

This has the symptoms of a wheel speed problem.  This ECU should store the
codes, but I don't know what the protocol is.  While the wheel speed sensor 
may be in good shape electrically there may be other problems such as; the
gap between the sensor and reluctor ring, contamination of the reluctor 
ring
with metalic particles, bad wheel bearing causing sensor gap variation.
Fortunately the ABS system is sensing a failure and you should be able to
use this information to help diagnose your problem.

Rich V.

Date: Fri, 28 Apr 2000 11:03:35 -0400
From: "Mike Turner/ENGR/HQ/KEMET/US" <MikeTurner at kemet.com>
Subject: [No EFI] ABS Help Needed

Where might one find any information on troubleshooting, communicating
with, replacing, etc. an ABS unit for a late 86 (ie 87) Corvette?

Ours has developed a couple symptoms. The first occurs just after mild
brake application. On release of the pedal, the abs kicks in and the pedal
starts vibrating for a short period. The other symptom is the ABS light
coming on sometimes after this event but not always. ABS action during and
after hard braking looks and feels normal.

I have considered a complete brake line flush including the lines to the
abs unit. Removal and replacement of the abs unit looks non-trivial to my
untrained eye. My local vette experts indicate fluid contamination should
not cause this symptom. A sticking pad or caliper could fool the abs (ok
the wheel may actually be locked up and abs is just doing its job but seat
of the pants says no wheels are locked since car is slowly rolling). Ditto
a flaky wheel sensor.

Additional info:
Calipers replaced a few months ago. Symptoms did not immediately appear
after replacement.
Brake pads are hawk autocrossers which squeal impressively.
Rotors are stock.


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