97urS6

I was getting an ABS fault saying the left rear speed sensor was not sending signal. Changed speed sensor, still getting the same fault.

Checked continuity in wires up to ABS Module and all seems to be good. So that left us thinking it was the ABS Module. So I bought a used replacement Module. Replaced the Module and recoded it... sure enough the fault went away! And the speed sensor was now registering properly. Everything was good!

Next morning we started to bleed the brake fluid, but we can not seem to get good pressure in the pedal? Going from wheel to wheel to wheel, pumping the pedal, open the bleeder, hold pedal down, tighten bleeder... just can't get good pressure? Is there some special procedure that is required to get the system up to pressure?

I looked through the beta online Bentley and couldn't see anything that would suggest a special computer based bleeding procedure or something out of the ordinary?

Any ideas?

J. Patterson

I use a Motive pressure bleeder on our Audis. Makes it a one man job and reduces the risk of pumping the reservoir dry and introducing air. Worth the $. It only takes a tiny bit of air to create a spongy pedal. Good work on the ABS module.

MP4.2+6.0

I still do it the old fashioned two man (wife) way--pump-release, etc. Nothing special there.

And yep, do not ever let reservoir run down or you play hell trying to get air out of ABS and good prime even on master cylinder.

97urS6

Thanks for the reply... ya, I have always wanted to get one of those Motive pumps. But don't have one. My buddy is suspicious of the pressure switch... on the vag we can see it fluctuating a bit from -1.28 to -0.6 while no one is touching the brakes. Not sure the units are?

So we are thinking that maybe we should swap back the original pressure switch? Not sure how that will help with the bleeding?

97urS6

Also, a quick question... when you activate the ABS pump with the Vag, and open a bleeder valve... should you get more fluid coming out the bleeders? We tried it and it just drips out, not much pressure ... we were kind of expecting it to come out with some gusto... but maybe not?

Shamoye Lewis

you should have just change the electric part on the back of the pump and not the hydraulic, save all this mess, the bleeding is going to be a mission you will need to fill the reservoir open the bleed nipple at each caliper until it starts to gravity feed leak, close them all off and start bleeding one by one going FL to RR to FR to LR then the two rear then last the two front... by this time you should be able to build pressure... pump 4 strokes then hold on each bleed, 3 - 5 bleed on each caliper....

J. Patterson

Sorry, can't help there. I've probably bled the brakes on my TT 20 times for track duty but I have never cycled the pump with VAG com. Others just get new fluid every couple of years. ( or three &#128521. Good luck purging that air bubble. Don't give up. Once a couple of years back I was bleeding brakes on a Cayman I had and got careless with the Motive and blew the reservoir dry and pumped air into the system. I had to put 2 liters of DOT4 in the Motive and REALLY give it a thorough flush starting at right rear and moving through each caliper towards the left front. There were bubbles forever till the fluid finally flowed solid and clear. The best part---- When I got done the brakes on that Cayman were firmer than the had EVER been before! Sometimes it takes a lot of fluid to push air all the way through.

MP4.2+6.0

For OP, you replaced just the electronics component of ABS correct? That is, not the whole hydraulic side too. There seems to be some confusion in the thread, so please clarify. And yes, from my own experience when I let the reservoir run too low once bleeding my C5, you would play hell trying to get it bled again to where it pumps normally. But, doesn't sound like you pulled the hydraulic side if I read it right.

97urS6

Yes, we replaced the whole ABS unit, not just the electronic Module. Maybe that is part of the problem? I'm pretty sure we never let the fluid reservoir go empty, but you just never know... we've been trying to bleed the system for hours!

MP4.2+6.0

So from my C5 experience, yes you will know play hell trying to bleed it. I have never used a pressure type system, but that is one obvious choice. Also look at whether VCDS can cycle the ABS system--meaning actuating the valves rapidly. I never looked for it in the D3 IIRC, but it was one of the things done w/ C5 to bleed it when things got tough like dry reservoir or opening lines around ABS. When I had to bleed it, I probably pumped hundreds of times to get anywhere; leave a caliper open too and let gravity do its thing over some hours. I also moved repeatedly from wheel to wheel to try to get somewhere. Also remember it's dual diagonal, so reservoir feed ties the diagonal corners together--meaning going left or right on either end does help w/ that first distribution "split" right off the master cylinder.

It eventually came back, but like 50x the normal hassles to get it restored, and not remotely like the "old" days of bolting in a new master cylinder that took just minutes to get fluid flowing through it.