Faulty ABS

[Bernard Littau]

Hi Mike,

I can see your point that if you need to buy the part, it's not really a
test.

If you are going to be messing about with a 14 year old car, especially an
Audi, it makes good sense to acquire some acquaintances with similar cars
and the like disposition to mess about.  One then goes to one of these
acquaintances and either pulls the known good part out of their car, or
better yet their bin of parts from Audi's they have dismantled.

The ABS is poorly documented as far as testing for the lay person.  Audi
uses a plug in analyzer to check the inputs to the ABS controller.  If the
inputs are good, they start swapping controller and relay.  I went through
all the inputs with an oscilloscope a few years ago, only to find everything
there was fine on my car.  I'd even considered a stimulator of sorts to test
and play with the ABS controller under the rear seat, but just didn't have
the time.

I was pretty much in your shoes a few years ago.  In fact, I too was
convinced the relay was fine, so much so that I swapped ABS controllers with
an acquaintance's car to test, but declined to swap the relay.  I eventually
went to another acquaintance and swapped the ABS relay, which cured the
problem, whereupon I purchase a new ABS relay.

I'm not saying that because my relay was bad that yours is too, but I am
saying you can waste a lot of time testing this stuff the hard way.  And
even then, because it is so poorly documented, you are still not sure
everything is correct or not.

Go find another Audi nut and shower them with beer.  Swap the parts.

Best,

Bernard

> Thanks again, Bernard. Unfortunately, swapping in a known good component
> would require me to buy one (new or used) which means that it's not really
> a test - I'm just replacing the components anyway. This is why I wanted to
> try and diagnose as much of the fault as possible first. I still believe
> that my ABS relay is working OK because when I switch on my diff lock (yes
> it has an ABS switch and manual diff lock control) the ABS relay clicks
> off, and on again when the diff lock is released. The ABS switch itself
> does nothing, but that could be just a faulty wire between the switch and
> the relay.
>
> According to the Bentley wiring diagrams, when the ABS relay is on, it
> provides power to one coil connection of the changeover relay in the
> hydraulic modulator. The other coil connection (the ground) should be
> supplied by the ABS control unit itself, but only if it thinks everything
> is OK. I haven't checked this connection - perhaps the control unit is
> providing the right signal, but it is somehow not getting to the
> changeover
> relay. More diagnosis required. The trouble is that I can't do much until
> the weekend because it's getting dark now when I get home. Stupid Autumn
> (Fall, to you guys in the U.S.A.)!
>
> Cheers, Mike.
> '89 200qta
>
>
>
>
>                     "Bernard Littau"
>                     <bernardl at acumenassoc       To:
> <Mike_Buckham at ptk.pioneer.co.uk>
>                     iates.com>                  cc:
> <quattro at audifans.com>
>                                                 Subject:     RE: Faulty
> ABS
>                     02/09/2003 19:21
>
>
>
>
>
>
> Hi Mike,
>
> The sensors sound like they are fine.  I think you should swap in a known
> good ABS relay -- I suspect that relay does more than just power up the
> hydraulic modulator.  After that I would swap in a known good ABS
> Controller.  If both of these prove fruitless, then I would suspect and
> chase after funky connections.
>
> I can't remember what the '89 has as far as diff and ABS control.  Does
> your
> car have the ABS off switch or manual diff locks?  Activating the diff
> locks
> will turn on the ABS light.  Make sure a diff lock is not on.
>
> Bernard
>
>
>
> This e-mail and any files transmitted with it are confidential and
> intended solely for the use of the individual to whom they are addressed.
> If you have received this e-mail in error please notify your system
> manager.
>
> Please note that any views or opinions presented in this e-mail are solely
> those of the author and do not necessarily represent those of the company.
>
> Finally, the recipient should check this e-mail and any attachments for
> the presence of viruses. The company accepts no liability for any damage
> caused by any virus transmitted by this e-mail.