[s-cars] Dash Brake Light On

Tue Sep 3 15:16:30 PDT 2019

Buried in https://forums.quattroworld.com/s4s6/threads/32748.phtml

 <https://forums.quattroworld.com/s4s6/msgs/359096.phtml> A lot of this was learned the hard way, but just as much came from forum members willing to share

Posted by: scarman <mailto:trgreen at comcast.net>  (7055 <https://forums.quattroworld.com/account/7055.phtml?page=/s4s6/threads/32748.phtml> ) on 2019-05-27 20:18:07 

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details not available anywhere else. I can't count the number of times I have sent guys from the list to Scott Mockery's SJMautotechnik.com <http://SJMautotechnik.com>  for how to handle an engine problem. Scott was in the automobile repair business but took the time to share many details of troubleshooting and repairing the 5cyl engines, including how to use the information from scanning fault codes. I wasn't an auto or airplane mechanic-I just liked fly them both. 

The owners manual lists the conditions that cause the BRAKE light to come on. Other than lifting the parking brake handle off the rest (and switch) the most common is low hydraulic pressure in the system measured at the power brake servo just behind the brake master cylinder. Many vehicles will develop a problem retaining the pressure in the brake assist hydraulic system after shutdown, requiring 15 to 30 sec for the pump to repressurize the system to the 2200 PSI minimum. The only electrical wire there connects to a pressure switch. You can remove the connector to check if low hydraulic assist is the cause of the light. The power brakes will still work normally at some lower pressures that are accompanied by the BRAKE light. This waiting a few seconds before driving off gets to be a routine habit with many owners. Hopefully, those have inspected the system for any leaking hoses, fluid levels, leaking pumps, etc. The brake assist hydraulics have a very small quantity of high pressure hydraulic fluid mostly stored in the bomb. One test says that the bomb should provide 30 power brake applications after engine shutdown. I would edit that to say that the perfect system will give you 30 uses, but you certainly want several if you have such an emergency on the road.

You want to avoid operating the car with the BRAKE light on, even coming on momentarily when the brake pedal is depressed, and especially if there is any pulsing of the pedal during braking--unless you are sure that the light is caused by low hydraulic pressure but plenty for several power brake applications. This is because the car is very difficult to stop without power brake assist, even at low speeds. Try it out sometime.

So, here we are. What exactly is causing that BRAKE light to come on? Well, frankly I don't know. I am too far away, but I wouldn't know if I had my head under the hood. This is the reason owners get frustrated with that BRAKE light coming on. To provide any answer, we need to back up, and look at what PM needs to be performed so this doesn't happen, at least until you wear out the pump after several years. There is no inspection 1 or 2 requirement to change fluid, but never let it get dirty to where the fluid loses that bright green sparkle ( or red in my Redline PS fluid). There is a screen filter that the float on the reservoir cap fits down in. It is a last ditch filter before fluid heads to the pump. It is a bright metal screen. If it is black, that is German rubber hose. If the fluid is the same dark color, drain it as completely as possible and put some clean fluid in there. You may want to remove the steering hose bolt and prime the pump with clean fluid there before starting up. 

This might help some. There are reports that after getting the reservoir at the proper level, holding the brake pedal firmly down for a minute or two can cause the pump to circulate as much pressure as it can through the system and maybe dislodge any of that black rubber from the bomb check valve or the brake servo that may have been allowing fluid return to the reservoir instead of closing to allow pressure to build. If this doesn't fix things, there are some small screens in some of the banjo bolts of the hydraulic system that can catch debris and restrict flow sufficient to cause problems. I have not mentioned that this is tedious and dirty work, and you need to clean up all this spilled fluid also, so you will know if a leak occurs.

You will probably get overwhelming advice to just change the bomb now, but that's $350. And, if that is wrong, the pump is another $450. This is getting serious. If you change any of these and/or steering rack or power brake servo, make sure the fluid is clean.

You really didn't expect to get a quick answer on this, did you? Part of the answer lies in just what the hydraulics look like under the hood. 

-Stott

-----Original Message-----
From: S-CAR-List <s-car-list-bounces at audifans.com> On Behalf Of Douglas Fifield
Sent: Tuesday, September 3, 2019 5:52 PM
To: Mike Claire <mike.claire at gmail.com>
Cc: s-car-list at audifans.com
Subject: Re: [s-cars] Dash Brake Light On

Mike,

The pedal feels normal. The car functions as one might expect. Rust on the disks. Brakes well.

D.

> On Sep 3, 2019, at 4:43 PM, Mike Claire < <mailto:mike.claire at gmail.com> mike.claire at gmail.com> wrote:

> 

> I sold mine like 5 years ago, but i remember the brake circuit!   Is the brake pedal hard?  If so, that could be the bomb (accumulator).  I think there's a test that involves backing off one of the brake lines on the master cylinder. 

> 

> 

> Mike

> '17 Q5

> No cool Audis though

> 

> On Tue, Sep 3, 2019 at 3:20 PM Douglas Fifield < <mailto:douglas.fifield at gmail.com%20%3cmailto:douglas.fifield at gmail.com> douglas.fifield at gmail.com <mailto:douglas.fifield at gmail.com>> wrote:

> Hedz,

> 

> Patient is a 95.5 S6 Avant who has been hibernating. I have resurrected it and am trying to fix all the little issues that go along with old sleeping cars.

> 

> The issue I need help with now is the resolution of the dash brake light being on. When I first started it up the light stayed on for a little while and eventually went off. Today, I took it out for some errand running and at first the light went off after starting the engine - until it did not. 

> 

> I need a quick refresher on what triggers that light. I have not touched the parking brake. That at least should not be an issue.

> 

> As always, thanks in advance to the collective mind out there.

> 

> Douglas in Duluth

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