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Discussion Starter · #1 ·
Recently I brought my 2002 Passat GLX into the garage due to a engine light. I was told I need a new coolant sensor which I told them to replace. Now recently after getting my car back I have noticed spongy brakes. The mechanic told me the coolant sensor was difficult to get at and things had to be remove to replace it. I'm wondering if during the maintenance they expose my braking system to air.

Also I'm wondering if adding brake fluid to the reservoir may help with the spongy brakes in case the brake fluid level is low. The reservoir is embedded in a covering and I can only see the MAX line and I can't where the brake fluid level is at. I also can't see below it where the MIN line is due to the covering. I tried adding fluid but is doesn't seem to want to take any. Maybe the fluid level was already above the MAX line high in the filler neck of the reservoir, its kind of dark out there. There is a screen in that opening with what appears to be some dirt. I'm also wondering what the other smaller port on the topside (the one with the screwdriver slot in the cap) of the reservoir is for. I openned that and fluid and some black stuff, similar to what's on the screen, flowed out over the top of the reservoir.

Any help would be appreciated.
 

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Can you take the car back and ask if they did anything to the brakes?

Maybe have them bleed the brakes to see if that fixes the problem.

If the brake fluid hasn't been changed it probably should be. I believe VW recommends changing the fluid every 2 years.
 

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I'm betting you need a brake flush, especially with that black crud on the screen and in the fluid that flowed out. Mine had some black sediment in the reservoir in less than 3 years - guess that's why they recommend changing the brake fluid every 2 years.

It's pretty easy DIY, especially if you use a power bleeder.
 

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Discussion Starter · #4 ·
Thanks for responding. After I posted I looked up replacing a coolant sensor and am kicking myself. I could have done it myself and saved myself a bunch of money. From the instructions I saw it doesn't appear any part of the braking system would be touched. It is probably just a coincidence that I have spongy brakes after that garage worked on my Passat. There is a lot of sediment in the screen of the reservoir so I will drive carefully and have the brake fluid flushed. I'm still wondering what the smaller cap on the reservoir is for, the one with the flat screwdriver slot in it. ?
 

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Thanks for responding. After I posted I looked up replacing a coolant sensor and am kicking myself. I could have done it myself and saved myself a bunch of money. From the instructions I saw it doesn't appear any part of the braking system would be touched. It is probably just a coincidence that I have spongy brakes after that garage worked on my Passat. There is a lot of sediment in the screen of the reservoir so I will drive carefully and have the brake fluid flushed. I'm still wondering what the smaller cap on the reservoir is for, the one with the flat screwdriver slot in it. ?
It's for draining the reservoir. You have the screen under the reservoir cap, so you can't drain it thru there. You drain it by unscrewing the yellow cap, attaching a small plastic hose to the port under the cap (IIRC there are two ports), and siphoning out the old fluid from the reservoir. You then add new fluid to the reservoir, so when you bleed at the calipers you are pushing/pulling (depending on your bleeding method) new fluid thru the brake system instead of the old fluid that was originally in the reservoir. It also obviously speeds up the process, since new fluid gets into the system sooner.

Suggest you siphon the reservoir, as well as bleed each caliper, into a glass jar - you'll probably be amazed at how bad the old brake fluid looks. If you bleed into a plastic container, or an oil drain pan, etc., you won't notice it as much, but in a glass container mine was absolutely filthy after 3 years.

I used a Motive power bleeder - best $45 I ever spent, and Valvoline Synpower DOT 4 fluid ($5). Total bleed time (by myself) was a little over an hour, but I was slow and careful. Dealer gets over $100 for a brake flush.
 

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My 1998 just hit 80,000 and is in the shop now getting the brake fluid flushed. I went down to the VW dealer, bought two $9 cans of brake fluid and agreed to a $72 service.

My brakes were fine, but if you can find a local knowledgeable VW shop, your spongy brakes might be fixed for less than $100. (If fluid is the problem -- which it could be.)

.... However, I don't think you should be opening your brake fluid container -- brake fluid soaks up water any time it is exposed to air, which decreases its performance. Sounds like you know this, but just thought I'd point it out. You should also clean the dust from around the brake fluid resivoir before opening it, as it will suck in all the surrounding dirt (maybe this is the black stuff you're seeing?)

If you aren't REALLY COMFORTABLE under the hood, brake systems, as simple as they are, probably isn't the first thing you want to be messing with...
 
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