Re: Brake Alert Light

["Fred Munro" <munrof@isys.ca>]

Hi Matt;

    Sounds like you have two different problems here.

    The orange brake pad warning triangle is typically triggered by a wear
sensor embedded in the brake pad. The "sensor" is a loop of wire which is
severed as the pad wears. Once the circuit goes "open", the warning triangle
lights up. Anything else which results in an open circuit ( connector not
attached, broken wire, etc.) will result in the warning illumination. The
free wire you have noted by the caliper probably should be connected to the
wear sensor and is resulting in the orange warning symbol. If not properly
routed and secured, these wires can be severed by rubbing on the brake disc.
    Some aftermarket pads do not have the embedded sensors. To shut off the
warning light, you have to jumper the two contacts in the sensor plug at
each front caliper.

    The most common cause of the red warning light under hard braking is low
hydraulic pressure in the brake boost system. This is usually caused by a
bad hydraulic accumulator (aka "bomb") and is a potentially dangerous
situation - brake boost can be lost in an emergency stop, resulting in
significantly reduced braking effect. Test the bomb by running the car to
charge the bomb, then stopping the engine. Pump the brakes until the pedal
gets "hard" (no more brake assist). A good bomb gives 30-40 applications, 10
or fewer and the bomb should be replaced. A bad hydraulic pump can also
result in low pressure, but the bombs only last about 7-9 years and are the
most common cause of the low pressure warning.

    The falling brake pedal may indeed be the sign of a failing master
cylinder.

HTH

Fred Munro
'91 200q  269k km
-----Original Message-----
From: Matthew Poynter <mpoynter@zoo.uvm.edu>
To: Quattro, Mailing List <quattro-digest@coimbra.ans.net>
Date: Tuesday, March 02, 1999 11:34 AM
Subject: Brake Alert Light


>On my newly-purchased 1987 5kqtw the orange brake pad warning light is
>always on. The previous owner said that a wire was missing which is
>causing this.  I inspected the pads and they are all pleanty thick.
>During this inspection I noticed a free wire that looks as though it
>should plug into the driver's side front caliper somewhare and there
>looks to be a fitting that retains this wure to a a location near the
>caliper.  Is the wire in question or have I "discovered" the outside
>temperature sensor?  Does anyone know what part I MIGHT need or what to
>call it?  Also, does this sensor being constitutively active cause my
>RED brake alert light to come on whenever I brake hard or are these
>things unrelated (the pedal is kinda soft and falls some if it remains
>depressed [like the MC may be not so good] but the brake and power
>steering [hydraulic] fluid are at the appropriate levels.)?
>
>Thanks,
>
>Matt Poynter
>