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General E46 Forum
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Old 09-09-2011, 10:16 AM   #1
e46frvr
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e46 brake fluid low

History: Alternator died, subsequently car came to a stop while driving. Right before car was bogging/shutting off: brake, dsc, abs lights come on. Replaced alternator, car starts up fine but brake light stays on (red) and dsc light comes on after a few mins of idling/driving. Just noticed the brake fluid was low (below the MIN level) which would explain the brake light, correct?

Questions..
1. Can the fluid possibly be low because the power died while the car was on and I had to step on the brakes to stop?
2. Can I just top this off with DOT 4 brake fluid from a parts store? Do I need to do a full brake flush? I dont have time to do a full brake flush right now. There should be no air since the brake tank isn't fully empty, correct?
3. Whats the simplest way to check for brake fluid leaks? Can I top it off, drive the car and simply watch the brake fluid levels?

Thanks

Last edited by e46frvr; 09-09-2011 at 10:17 AM.
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Old 09-09-2011, 10:45 AM   #2
jcns
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1) possibly low but not related to your incident
2) yes, you can top it off. However, if your pads are thin when you replace them the fluid may go past the "MAX" limit. This can be addressed with bleeding the system.
3) Follow the brake lines and look for darker/wet/damp spots.

Your problem is something else. Pull the codes first.

Last edited by jcns; 09-09-2011 at 01:31 PM.
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Old 10-10-2011, 09:43 AM   #3
e46frvr
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Bump. Just got back from a long vacation so looking at this now...
The check engine light is not on. Just the brake and dsc lights. Will there still be codes? (Can autozone get these codes for me? Or is it the special BMW tool/software?)

About a year/2k miles ago, there is the following entry in the service records...
"Traction Control Light on. Brake light on. Brake fluid is entering brake booster."

What does this mean? And how can I check if this is the problem again?

Thanks
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Old 10-10-2011, 10:09 AM   #4
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I'm just curious

As you were driving along did you not notice one system after another shutting down? First the alternator light comes on, and then one system after another refuses to respond as they sense the voltage dropping below the level sufficient to operate. Power windows sluggish, etc. Ask me how I know? Because this happened to me many months ago and I experienced all this driving along Rt 80 trying to make it to a Welcome Center where I could wait comfortably for the tow.
Replaced the alternator and then drove directly to Autozone to replace the battery because they are never 100% after being fully discharged and I didn't want to fool around. Guy was kind and gave me a huge benefit of the doubt rebate, so new battery cost me about $40!
Moral of the story is make sure your battery tests completely good because wacky voltage can cause strange symptoms.
If the brakes feel good, probably OK to drive while carefully frequently monitoring the brake fluid level. I'd also want to have a conversation with a BMW mechanic to see if they express any urgency toward testing or replacing the brake boost? Perhaps this was already done?
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Old 10-10-2011, 11:25 AM   #5
jdstrickland
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The brake fluid is low, that's one problem. The car died, that's another. They are not related.

Brake fluid entering the brake booster is one of the few times the brake magter cylinder will develop a leak to the oustide. NORMALLY, the master cylinder will develop leaks internally, and this is presented to you as a sinking pedal as you wait at a traffic light. The master cylinder consists of a body that is bolted to the car, and a piston that moves, and is attached to the pedal. The piston has o-rings to seal the space between it and the body. The o-rings fail, fluid leaks into the space that is supposed to be sealed, and the pedal sinks. You never see this on the outside.

If the fluid in the reservior is falling, and the brake booster is filling, then you have your answer...
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Old 10-10-2011, 11:43 PM   #6
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I wouldn't use brake fluid to top off, it might be ATF if I'm correct??
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Old 10-10-2011, 11:53 PM   #7
Stinger9
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It's not so disturbing to us Kwaz that you

don't value your own life, but that you don't value ours either perturbs me.
ATF in the brake reservoir puts us over the edge of the cliff. I'd rather not go there myself.
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Old 10-11-2011, 12:08 AM   #8
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My bad I meant power steering
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Old 10-11-2011, 05:45 AM   #9
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Quote:
Originally Posted by e46frvr View Post
Bump. Just got back from a long vacation so looking at this now...
The check engine light is not on. Just the brake and dsc lights. Will there still be codes? (Can autozone get these codes for me? Or is it the special BMW tool/software?)

About a year/2k miles ago, there is the following entry in the service records...
"Traction Control Light on. Brake light on. Brake fluid is entering brake booster."

What does this mean? And how can I check if this is the problem again?

Thanks
I guess the entry was made by PO? If that's true, that might be why your brake fluid is low.

If you're free this Sunday, bring the car to IMG and I'll get someone to look at it for free. Check the regional thread--we're having a DIY meet at this shop, and there will be real mechanics there. That said, you need to monitor brake fluid level well and if Union, NJ is a long drive for you, I'd search the regional forum for a good local indy. It seems like the issue is a small leak, as otherwise, I suspect you would have lost Power braking a while ago.
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Old 10-11-2011, 10:07 AM   #10
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We're just having fun

I knew you wouldn't have done that.

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My bad I meant power steering
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Old 10-11-2011, 11:41 AM   #11
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Quote:
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I wouldn't use brake fluid to top off, it might be ATF if I'm correct??
No, you are not correct. In fact, you are fatally wrong. You do not put ATF into the brake reservior. You do put either ATF or Power Steering Fluid -- depending on the auto maker -- into the power steering reservior, but except for you, nobody is talking about that.

PS
BMWs take Dexron III transmission fluid in the power steering.
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Old 10-11-2011, 02:07 PM   #12
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Your abs and dsc lights come on when the master cylinder gets low. Probably 95% of the time when the fluid is low, the brake pads are worn down. If you top it off, the next time you do pads and push the piston back into the caliper, brake fluid will explode from the cap on the master cylinder. Check your pad wear before topping it off.
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Old 10-15-2011, 11:41 AM   #13
e46frvr
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Brake pads are quite good - I visually checked all four. They doled out a healthy dose of brake dust days after I washed the car. Ugh.

Anyway, I looked at the service records again and this is what I see in the service records (bmw dealer - 1.5 years back)
"Brake light on. DSC light on. Brake fluid was low. Brake fluid entering brake booster. Customer declined repairs"

Since the symptoms are similar, I assume the previous owner didnt get the problem fixed.
I tried doing a search on brake booster and I see the problem can be several things from seals to hoses etc.

Three questions
How can I confirm fluid is indeed entering the brake booster?
How do I figure out what to replace related to the brake booster? Full unit? Hoses? Seals? (My car has 25k miles and its a 2002 model FYI - so low miles = seals?)
I understand there is a risk of letting air into the ABS and DSC units. What is the concern here? Will the light come on and I can drive it to a shop with GT1 to get it looked at? Or should I not even drive with air in the ABS and DSC units?

Thanks! Sorry for any noob questions

Last edited by e46frvr; 10-15-2011 at 11:53 AM.
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Old 10-15-2011, 12:06 PM   #14
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Simple; bad brakes can get you killed

The conservative advice would be to not drive your car at all if your brakes are in question. I don't know how far your dealer is or how your car feels to drive right now.
But with this problem I would want to get some expert diagnosis, repair this problem, and put this behind me. I'd not want to think that at any time into the years ahead, I might lose my brakes

Sounds like your car is in good shape and with low miles it could be a winner for you. But yes any system can completely fail even with low miles. Especially with years of parts just aging naturally. Nine years old now.


Quote:
Originally Posted by e46frvr View Post
Brake pads are quite good - I visually checked all four. They doled out a healthy dose of brake dust days after I washed the car. Ugh.

Anyway, I looked at the service records again and this is what I see in the service records (bmw dealer - 1.5 years back)
"Brake light on. DSC light on. Brake fluid was low. Brake fluid entering brake booster. Customer declined repairs"

Since the symptoms are similar, I assume the previous owner didnt get the problem fixed.
I tried doing a search on brake booster and I see the problem can be several things from seals to hoses etc.

Three questions
How can I confirm fluid is indeed entering the brake booster?
How do I figure out what to replace related to the brake booster? Full unit? Hoses? Seals? (My car has 25k miles and its a 2002 model FYI - so low miles = seals?)
I understand there is a risk of letting air into the ABS and DSC units. What is the concern here? Will the light come on and I can drive it to a shop with GT1 to get it looked at? Or should I not even drive with air in the ABS and DSC units?

Thanks! Sorry for any noob questions
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Old 10-15-2011, 12:12 PM   #15
e46frvr
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The conservative advice would be to not drive your car at all if your brakes are in question. I don't know how far your dealer is or how your car feels to drive right now.
But with this problem I would want to get some expert diagnosis, repair this problem, and put this behind me. I'd not want to think that at any time into the years ahead, I might lose my brakes

Sounds like your car is in good shape and with low miles it could be a winner for you. But yes any system can completely fail even with low miles. Especially with years of parts just aging naturally. Nine years old now.
Thanks but I should have clarified.
The questions above are unrelated.

I meant to say - AFTER I fix the the brake booster problem, what if there is air in the system. Will I harm the DSC and ABS systems driving it like that? I fully understand the implications of air in the brake fluid and will ensure to bleed properly. I was just worried about air entering the DSC and ABS units (also, if air enters these units, I understand a pressure bleeder cant get it out but will the ABS and DSC lights go on?)
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Old 10-15-2011, 12:23 PM   #16
Stinger9
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I do not think that air in a system

in proper operating condition would hurt anything. Especially if you drive easy.
I have read that air in an ABS system requires a dealer computer to open all the valves so it can be bled properly. The implication being that if air is trapped in the system, it can remain trapped in pockets of the ABS system that normally do not open except in the case of panic stops where the system reaches the electronic pumping mode.
This is an interesting question that I will try to remember to ask my dealer mechanic next visit. Wonder if there is anything on the TIS regarding this.

Quote:
Originally Posted by e46frvr View Post
Thanks but I should have clarified.
The questions above are unrelated.

I meant to say - AFTER I fix the the brake booster problem, what if there is air in the system. Will I harm the DSC and ABS systems driving it like that? I fully understand the implications of air in the brake fluid and will ensure to bleed properly. I was just worried about air entering the DSC and ABS units (also, if air enters these units, I understand a pressure bleeder cant get it out but will the ABS and DSC lights go on?)
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