Andei a investigar mais um pouco e cheguei ate isto:
um video no youtube do que se passa na minha carrinha
https://www.youtube.com/watch?v=glZMXFXnbI8
depois pelos comentarios e forum cheguei a um post de um documento que parece da audi.
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I can't see it being this issue, it should have been dealt with six years ago.
Technical product information Transaction No.: 2014619/4
Brake fluid warning after cold start - A4 RHD, MY 01-07 Release date: 11-Dec-2009
Customer statement / workshop findings
At cold start the red brake warning light comes sporadically on. Vehicles with big diesel engines are particularly affected.
User profile: “ Customer in a hurry” ; turns the ignition key without waiting for the glowing period.
Technical background
Magnetic coupling from the starter motor cable to the switch for brake fluid level. As a result, a too low brake fluid level is incorrectly indicated.
Production change
New software (version 0200) in the dash insert from week 45/06.
Measure
Fit an extra relay which separates the switch for brake fluid level from the dash insert when starting the engine.
How it works
A relay is fitted which is controlled by terminal 75. Before the start of the engine the relay drops thus separating the signal cable between dash insert (point 4 in illustration 1) and switch for brake fluid level. As a result, the signal of the brake fluid level is disrupted during the start.
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ja alguem ouviu falar alguma coisa disto??
alguma forma de resolver?