Something's up with my car's brake system but I don't know what.

February 4, 2012 4:33 PM

Can someone help me figure out why my car is acting up? It's starting to drive me insane. It's some issue with the brake fluid system, I think, but I'm not sure.

I drive a 97 Aurora Oldsmobile that I got for a thousand bucks. It's lasted well over thirty thousand miles at this point with only minor issues with the coolant system and general wear and tear. But since the beginning of winter, there's been a new problem that is slowly driving me crazy.

Every time it's icy/snowy out and my car starts to lose traction, the ABS light and the Brake Fluid light will come on. Sometimes they only come on for a moment, but eventually they come on and stay on and my car starts emitting a constant chime that gets on my nerves. I've been dealing with it for a couple months and now I'm just getting murderously angry about it.

I did some sleuthing and found out that it may possibly be the brake fluid level sensor that's causing the problem. But then I don't understand why it only happens during the winter and only when I lose traction. The way that I checked this was by removing the cabling attached to the master cylinder to see if that turned the light off, which it did. That's what the internet told me to do, anyway.

If it is the brake fluid level sensor, the way my car is, it looks like I'd have to remove the master cylinder to get into everything and I don't have that kind of technical skill nor do I have much money to get it serviced. If this turns out to be the problem, could I unplug the cabling so I didn't have to deal with the incessant chiming?

posted by Modica to travel & transportation (11 answers total)

It sounds to me like you have a slight leak in one of your brake lines. Your car is the right age for it. The ABS system often pumps the brakes during a traction event.
Take it in and get it fixed now.
posted by rfs at 5:13 PM on February 4, 2012

Well, the first thing I would advise is to make sure that your brake system is OK. No leaks, no broken lines or swollen hoses, all the seals in good shape. Brake fluid is full and not contaminated with moisture.

As I recall one the olds, it uses the ABS system to arrest wheel slip, resulting in power deliver to the other tire. So yeah, barring an actual fault (Low fluid, etc) then a fault reading must imply a faulty sensor.

I don't know what the effect of just unplugging the sensor would be. At the most benign, it would merely disable the ABS and TCS and put some annoying lights on the dash. At worst, it could put the car into limp mode, which severely restricts its performance.

If it were me, I would replace the sensor - brake work isn't that hard; bleeding the system is the worst of it and its pretty easy once you get the hang of it. If you don't feel confident doing it, I'd recommend having a professional take a look at it and/or fix it.
posted by Pogo_Fuzzybutt at 5:19 PM on February 4, 2012

When you open the reservoir it's full and you're not adding brake fluid during this, right?

I just had issues with my Volvo and the "brake fluid" light is pretty much the "hey, something or another is wrong with your brakes" light, so it might not be your fluid sensor at all. (In my case it was a damaged wire to a wheel speed sensor.)

If you can figure out where all of the wheel speed sensors and the fluid level sensors are connected, I would try unpluging them and plugging them back in to maybe clean up a dirty contact somewhere. In the Volvo, there are some solder joints in the ABS control module that tend to crack, and now, quite the little cottage industry where guys will carfully saw them open and reflow the solder for you for about $100. (This could be exaplained by the cold too - things expanding and contracting and ok contact becomming not quite good enough contact.)
posted by Kid Charlemagne at 5:47 PM on February 4, 2012 [1 favorite]

Have a garage get the fault code from the ABS.
posted by zippy at 5:58 PM on February 4, 2012

Yes, the reservoir is full. I added brake fluid the first time it happened, months ago, thinking that the fluid was the actual problem. Haven't added any since.

The liquid is all sorts of murky and gross, though. I'm wondering if things need to be changed out altogether anyway. I don't know how to do that, though. I'm not too skilled with cars. For example, I have no idea where to even begin looking for the things you just mentioned.
posted by Modica at 5:58 PM on February 4, 2012

Sounds like a brake fluid 'flush and replace' is in order in any event.

Have the workshop check out the brakes when they do this, at least to ensure you are not going to have the brakes take a holiday just when you need them.

They should be able to at least point you at a solution to the problem even if they can't fix it on the spot.

If you do it yourself, jack the car up on axle stands, take the wheels off and have a good look around to see if you can spot any signs of wet patches around the brakes and back of the wheels. Flushing and replacing the brake fluid is a good start to troubleshooting, as well as a good thing in its own right.

It's not hard, google will help, and having a mate who knows how to do is a double benefit, because it is best done with two people.
posted by GeeEmm at 6:41 PM on February 4, 2012 [1 favorite]

Brake fluid should be clear. If it is murky, it is contaminated.

A quick overview - Your brake system is a hydraulic system. The brake fluid itself is designed so that it does not compress - that way, when you step on the brake, all the power is transferred to the squeezing the brake pads together, and little of it is wasted on squeezing the fluid.

Over time, that fluid in the resovioir picks up contaminants - moisture, dust, etc. That stuff diminishes the ability of the fluid to transfer energy from the pedal to the brakes. So, it should be replaced periodically.

The way this is done is by bleeding the brake system. there are lots of videos on this You need to be careful when doing this, because getting contaminants or air into the system will require additional bleeding to remove.

But I would start with that. It's not hard - fact, its really simple to do.
posted by Pogo_Fuzzybutt at 6:46 PM on February 4, 2012 [1 favorite]

The ABS unit could just need to be bled. Or, that's a specific ABS error code and not an indication of low fluid.
posted by gjc at 6:56 PM on February 4, 2012

As the brake fluid absorbs water (DOT3 fluid is hygroscopic) its freezing point increases. I wonder whether your brake fluid is to the point that it is freezing locally. If so, you would start getting intermittent warnings because the wheels' behavior as stated by the tone generators (toothed sprockets) wasn't in accordance with your command. I'd do the following:

1) change brake fluid.
2) follow pogo_fuzzybutt's advice.
3) pull codes.
4) if and only if you have not resolved the issue by this point, replace the level sensor.
posted by jet_silver at 7:14 PM on February 4, 2012

nthing brake fluid leak, but also consider the possibility of contaminated brake fluid that is not necessarily leaking. I had an issue with contaminated brake fluid in my previous car, and two corroded and destroyed calipers later learned that it is in fact a serious issue that should be immediately remedied.
posted by labandita at 10:29 PM on February 4, 2012

You may have a leak somewhere in the system, such as a caliper piston seal leak or (if there are drum brakes on the rear) a leaky wheel cylinder. You may also have brake pads that have gotten very low. Before you dismiss this as a bad sensor, you really oughta get this looked over by someone who understands what they're seeing. The murky fluid is something of a red flag there.

I understand that you don't have a lot of money right now, but evaluate this one carefully. A brake failure on the road can be a lot more expensive.
posted by azpenguin at 9:24 AM on February 5, 2012