Re: [No EFI] ABS Help Needed

[Shannen Durphey <shannen@grolen.com>]

1986 Corvette does not communicate with a scantool.
Shannen

Malcolm Robb, LC 0112G wrote:
> 
> 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@hotmail.com]
> Sent:   Tuesday, May 02, 2000 12:53 AM
> To:     gmecm@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@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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