ABS? Brakes continually pulsing.

[lerxst]

First, here's how normal operation used to be:

Start car, Warm up, Once speed > ~8mph, I hear a "wheeee" really softly, and feel pressure from the brake pedal increase almost unnoticably. I assume this is some set/reset condition because it only does it after the car is started, never again until it's turned off and restarted.

Here's the problem:

Now, I start the car, and immediately feel pulsing from the brake pedal (feels to be in sync with the engine). It stops pulsing for a split second, then starts again. I verified pulses to be in sync with the engine, when I rev the engine at stand-still, the pulse frequency on the brakes increases with the engine speed linearly. There is no noticable "set/reset" noise when speed > ~8mph, and the car is almost impossible to stop using the brake pedal. The emergency brake works fine, and the car stops as normal.

This makes me think that somehow, for some reason, the ABS is in a perpetual "Triggered" position. It thinks it's braking and slipping all the time, even when I'm not braking.

Audiworld forums (and searching here) turned up nothing, but on Audiworld, there were a few similar cases that pointed to (and were resolved by) people with a bad brake switch (pedal) causing the car to think it's always braking, triggering the ABS, and replacing that switch. Other (not immediately noticable) symptoms included a constantly indicating brake light set on the back of the vehicle.

I just had a friend sit in the car and work the brakes with the car Off, On (without engine running) and Running On (with engine running). Brake lights operated as they should.

Any ideas where I should look? The drive home is going to be tricky and dangerous tonight, and hopefully, someone will recognize these symptoms, reply to this forum, and even more hopefully it will be good news and something small i can clean replace, set, reset, or kick... otherwise I've gotta find a card that i can charge $2k to and hope the small town mechanics know what they're doing. *shudder* :/

Thanks in advance,

-jre

[lerxst]

I should add:

1995.5 Audi S6Q Sedan. 117k miles.

[lerxst]

Ok. so. I feel dumb.

It's a 1995. Some of the dash bulbs are blown, that's to be expected.

I ordered a bulb ket from blauparts.com and haven't put them in yet.

If I had, maybe I would have noticed...

that when I pulled the e-brake, the brake lamp in the dash no longer came on!! So, I replaced it.

After this, I noticed it was on constantly.

A look-up of why this lamp would come on versus the brake indicator in the LCD matrix indicates two interesting things.

1) brake fluid level switch - i topped of my brake fluid, no change.

2) hydraulic fluid for the pump has a level switch as well... why is this important? Steering and braking! according to http://www.elektro.com/~audi/audi/bombrepl.html (last paragraph) this pump has two outputs and one return. one output feeds the steering assist, and one feeds the brake assist.

I decided to get more fluid.

On my way there, i noticed that my power steering was a little louder around slow corners.

it all started to make sense.

i put the fluid in, and after the ~8mph set/reset "wheeep!" sound, the brake lamp went out and the pulsing faded off. More importantly, the brakes worked well.

So... here's what happened...

the hydraulic fluid reservoir level was not great enough to have it feed to the pump. The pump was therefore not feeding the steering assist or braking assist well, and the braking assist was pulsing with pump revolutions, which are tied directly to engine speed, hence the linear synchronization. Also, the power steering was beginning to whine. Returned this level to normal, and everything is good.

Important: Audi recommends G 002 0000 (the famous green goo 2000) as mineral hydraulic fluid for this reservoir/pump. As a suitable replacement, I found a green can at a specialty auto parts store for $27 that was in english on one side and german on the other (makes sense, no?) that had the green goo inside of it. It was CHF 11S (that is apparently the name of the maker?!?) and it did seem to work. As a precaution, I am having the system inspected Monday by my favorite tech crew (they were busy, it's an unlucky friday, and they're closed on the weekends..). If there are further issues, I'll post them here, but it sounds like they think I did well, so if anyone else experiences this... and you don't know whether or not your BRAKE indicator is working or not (had I seen it, I would have immediately thought of level checks for fluids... but it was burnt out!) ... check that first. a shyster mechanic could have very easily replaced and billed me for a new pump, power assist module for brakes (perhaps steering as well!) and other things.

final cost: $27.

avoided costs: $1500+ ?

-jre