2008/9 2.0 TDI Caga very hard brake pedal

[Sam72662]

I’ve been doing some work on a good friend of mines and 2008 A4, the engine code is CAGA.

Following a full service of the car by myself I was also going to try and have a look at the braking system as the pedal is super hard.

Yesterday I did a quick test of the pedal pumping a few times when off and starting, the pedal was rock solid when off and only gave a tiny fraction when started.

I proceeded to pressure bleed all brakes, there was air in the system but about as much as you’d expect for a brake system that hadn’t been flushed for years. All pads and discs are ok.

This only improved the braking force slightly as we knew the sponginess would be a different symptom , and the pedal is still very stiff.


So my next thought is potentially the brake booster? Or a vacuum leak? Or maybe master cylinder but I haven’t really heard of an MC failure.

In terms of a vacuum leak, I cannot hear any hissing stereotypical of a vacuum leak. But there are symptoms of other items that I believe are vacuum assisted. P2015 error and P2563 error but these started throwing up way before the braking issue.

So I would love some help with a diagnosis if others agree or can shed some light on other causes of a very stiff brake pedal on these cars. Or potentially somewhere I can get a diagram of the vacuum setup? Or any other tips in general to help me diagnose the problem.

Any opinions would be massively appreciated, as I’d rather avoid them having to spend money on a brake booster and MC if needed.

Thank you!

[Larhal]

Sounds like you brake system is locking up. Are the wheels free to turn? I would flush the system to see if you have flow to each of the brakes. If so it would be the MC.

[mickeybo]

the problem with your hard brake pedal lies with your break servo either vac or servo

[Sam72662]

the problem with your hard brake pedal lies with your break servo either vac or servo


Thanks this is what I’m leaning towards, the brakes were flushed completely also.

[Crasher]

Says vacuum system problem to me, do a vacuum test on the pumps output to see if it will hold a vacuum.

[Sam72662]

Thanks, I’ll get a vacuum test underway. Does anyone know where I can find a diagram of the vacuum lines if there is a faulty hose somewhere? I don’t fancy spending hours playing follow the hoses!

On these cars is it a case of just testing the output and does anyone know what I should be looking for as a healthy PSI?

thanks for the help everyone

[Crasher]

The diagram will be on erWin, for first time users I recommend a €30 day rate to give yourself lots of time to download and save as a pdf all your cars info, the current flow (wiring diagrams) can take an hour alone. You will need a print to pdf app.

[Sam72662]

Thank you!!

I’ve registered and I’ll get a look for the day and download everything might as well!