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Discussion Starter · #1 · (Edited)
I'm in the process of diagnosing this pump on my 2004 VR6 (Petrol).
This pump is used on a lot of vehicles and on different Touareg models (V6 and V8 Petrol + Automatic gearbox).
So I thought I'd put all the literature here for any future troubleshooter :)
This is gonna be a thread of ramblings and official info and diagrams and fixes and tests and all the good stuff.
Let's start with a pic of the beast:

Last updated version for both LHD and RHD is: 8E0927317H. Price is around 360€. Cheaper aftermarket or used but I would be careful buying an unknown brand as this is a critical item.

244711


244712
 

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Discussion Starter · #2 · (Edited)
Let's start with how it works. Here is a PDF from HELLA. I'm still not sure it's the exact same pump. Will check all that later but the description fits my understanding :)

Under certain driving conditions or depending on the engine layout, no vacuum or an insufficient vacuum is supplied to the brake booster through the intake manifold of the internal combustion engine. The UP 28 variant can support the system by generating an additional vacuum (support application). The UP 5.0 can provide the pneumatic vacuum supply as a "stand-alone" system. For this, the pump acts as the sole vacuum source and ensures an adequate supply for the brake booster and any auxiliary consumers.

And from the VW Pump SSP:

Cars fitted with a petrol engine in combination with an automatic gearbox which comply with the EU 4 Standard have an electric vacuum pump. This is used for assisting the brake servo unit. In this engine-gearbox combination, the throttle valve is opened particularly wide when the engine is started from cold, as well as when it is idling with a drive position engaged and the brakes applied. This is intended to reduce the pressure drop in intake manifold. The reasons for this greater opening of the throttle valve is the heating-up phase of the catalytic converter after a cold engine start, as required by the EU 4 emission standard, and compensating for the greater torque friction (resistance in torque converter) which exists under the conditions mentioned above. Depending on the particular car model, two different versions of the electric vacuum pump are fitted:
1. open-loop controlled vacuum pump
2. closed-loop controlled vacuum pump
 

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Discussion Starter · #3 ·
And this is a quick way of testing whether the pump works or not. But testing whether the pump is working mounted as it should within the braking system involves more steps. More on that later:

 

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Great info!
However, often missed are the press fittings over plastic barb ends. 7L Eggs are old enough for the plastic to lose its elasticity and form heat cracks. It is the major contributing factor in Brake Assist system malfunction.
Then, of course, there might be issues with wiring, connection, and with the pump itself.

I've found all but two joints of the Brake Assist System on my 04MY compromised.
 
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