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Old 3rd July 2019, 10:02 PM
ainarssems ainarssems is offline
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Join Date: Aug 2010
Location: Rushden, Northants
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Quote:
Originally Posted by HPsauce View Post
I know it's a D3 not a D2, but a problem I (and others here) have with some of our D2s is serious lack of power, accelerating very gently and holding gear changes back. Typically after stopping at a junction (sound familiar?).
This is caused by a very tiny maladjustment of the brake pedal switch which actually has two switches internally; I wouldn't be surprised if the D3 was very similar.

One switch basically operates the brake lights, the other informs the ECUs that the brake pedal is depressed. There is a tiny bit of movement between the two actuating and it is possible to release the brake pedal, removing brake pressure and turning off the brake lights yet still telling the ECU the pedal is being pressed.

It's possible to see this happening very easily by monitoring the relevant channels with VCDS and gently operating the brake pedal. It can be even more obvious with the engine off as there's no servo to magnify foot pressure.
On my S8 this would typically occur after a gentle stop, with the brake pedal only depressed very slightly and released softly. After a heavy braking it would spring fully back and both switches would change effectively together.

The D2 solution is to adjust the brake pedal switch by screwing it in the appropriate direction. Bit of a swine to get at but do-able.

I know many later Audis (and other cars) have "set once" brake/clutch pedal switches with a very specific installation procedure so that may not be an option on a D3, but VCDS could still be used to check how sensitive they were and if they ever "stuck".
It may be the case but I think it's more to do with ESP seeing brake on and sending torque reduction request to ECU, it's not a rally car so it does not expect brake and accelerator to be pressed at the same time and then the D3 tech is not that recent so it takes a bit of time for ESP to see brake released and to cancel/modify torque reduction request to ECU. My D2 S8 does not have ESP so does not experience any of this, ECU only get torque reduction request from TCU when switching gears.
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2006 A8 Sport 4.2TDI quattro SOLD,
1997 S8, reached end of life with gearbox failure
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