Brake Pad Indicator Light

[Max Hoepli]

I tried by the instrument cluster, just behind the OK indicator light,
disconnecting the 3rd of the 8 terminals, the red/white wire from Auto Check
Main Control module pin 32, and no light will turn on at all. Experimenting.

Max

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of DeWitt Harrison
Sent: Friday, May 10, 2013 23:59
To: Quattro List
Subject: Fwd: Brake Pad Indicator Light

Don't know if anyone still cares re this 5000 brake pad indicator issue,
but I finally dug out the factory manual.

There seem to be pad wear indicators for only the front brakes -- the
important ones. The pad wear sensing circuit wiring runs as follows: one of
the right-side pad connections (connector T-2q/1) goes to ground; the
second right-side pad connection (connector T-2q/2) goes to the left side
pad (connector T-2h/2); the second left-side connection (T-2h/1) is an
input to the Auto Check Main Control module (pin 21). In short, so to
speak, this detection circuit is a series circuit so that a break at any
point, such as a pad which has worn through the "sensor" conductor, would
remove the ground connection from the Auto check pin.

Grounding the correct wire of the left-side pad wear indicator circuit
would result in an "ok" signal to the Auto Check system, but it would
ignore the right-side pad status -- not that this would be important given
that pad wear detection is not relevant under the given circumstances. So
bottom line: pin 21 of the Auto Check module (located behind the dash on
the passenger side) must be grounded in order to extinguish the warning
light. As mentioned on the qlist also, the break fluid level switch might
also be an issue (Auto Check control unit pin 5) supplying a ground signal
and the hydraulic level switch (Auto Check control unit pin 25) supplying a
ground signal might be alternate problems.

Best luck,

DeWitt Harrison
1988 5000CS

---------- Forwarded message ----------
From: DeWitt Harrison <dewitt635 at gmail.com>
Date: Wed, May 8, 2013 at 8:26 PM
Subject: Re: Brake Pad Indicator Light
To: Quattro List <quattro at audifans.com>


On Tue, 7 May 2013 21:29:31 -0400
"Max Hoepli" <mhoepli at vif.com> wrote:

> The brake pad indicator light illuminates. The wires off all the brake
pads
> are not connected. The wires on the right side are connected together. The
> wires on the left side are connected together and grounded. When the light
> once illuminated 2 years ago the left and right wires were connected to
each
> other, but then I additionally grounded the left side wires which caused
the
> brake pad indicator light not to illuminate. Now it illuminates again. How
> to fix? I have the Bentley Manual.

It should not have been necessary to ground any of the brake sensor wires
so I suspect there could have been an additional problem at the time each
pair of sensor wires was disconnected from the brake wear connector and
spliced together. I don't have the wiring diagram in front of me so I don't
know what the effect of grounding the left side wires might be nor wiring
details. Assuming nothing has been damaged, it's a likely a matter of
ringing out the wiring, one wire of the eight at a time, back to the fault
indicator system, to find the open circuit.

DeWitt
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