Suddenly lost all brake pressure! 2012 Hybrid

[muayad925]

Hi I have a 2012 M Hybrid with 132k miles, my brother was driving the car and was trying to brake to stop the car, and the brake pedal lost all pressure and the car woudnt brake at all. Thankfully he wasnt going fast and was able to stop with the E brake, but this could be a really fatal problem, imagine if I was going 80 on the freeway and wasnt able to break. It only happened once and the brakes were fine after that, I dont know what it could be. I changed the rotors and brake pads 5000 miles ago but I never experienced this problem. What could this issue be? The brake fluid is fine.

[JCesar]

did you notice any fluid on the ground or around the lines and brakes? you probably have a leak so look around and will be able to find were all the fluid is going to

[EdBwoy]

I am thinking it's a failing booster pump, but the intermittence of your problem would make the diagnosis, even at a dealership challenging.

I recall this member had a lot of trouble and ended up turning the car in:
help-2015-q70-intermittent-brake-malfun ... 05098.html

[muayad925]

I am thinking it's a failing booster pump, but the intermittence of your problem would make the diagnosis, even at a dealership challenging.

I recall this member had a lot of trouble and ended up turning the car in:
help-2015-q70-intermittent-brake-malfun ... 05098.html

You think if I change my brake booster plus master cylinder ill be fine? I found both parts together for 180 on ebay.

[muayad925]

did you notice any fluid on the ground or around the lines and brakes? you probably have a leak so look around and will be able to find were all the fluid is going to

Theres no leaks from what I observed.

[Larz]

I am always perplexed that we sometimes try to 'guess' and spend money and time replacing parts without actually knowing what's wrong. I know there are plenty of things easily diagnosed and fixed but when we aren't sure .... Just take it to the dealer. You are never locked in and forced to pay them to actually DO the repair. But you will get a trained technician who has experience with your car to diagnose and provide the name (and most times part#) that needs replacement. Just simply tell the service rep that you can't afford a repair of that price today, and you will return when you have the funds. Sure, they may charge you $100 for their time, etc. But here we are guessing $180 for parts and hours of your own time without even knowing if this is the fix. What if it's one of a million sensors that these beasts use? That could be a cheaper, easier fix in the long run.
Am I wrong to look at these things this way?

[ca18det_boy]

I agree with Larz that some things are better left to the dealer to diagnose, however this one you can test a bit before you shell out the dough to a dealer. My gut is saying master cylinder, master cylinder, master cylinder. Here is why, if your booster goes out the typical symptoms will be a hard pedal. Your car will still stop, but you'll have to press like hell to get it to slow down quickly. If the master cylinder goes out, you'll lose the pressure needed to apply the brakes and the pedal will fall to the floor. Now it is possible to pump the brakes and it will build up enough pressure to stop the car, but for the most part your pedal will feel spongy. Here's how you can go about figuring out if either of those parts are bad:

Booster: Start the car with your foot relatively firmly on the brake pedal. If the pedal falls a bit, this is a good sign. If it doesn't fall, then you're looking at a possible booster issue. Next, go under the hood. If you have a hand held vacuum pump you can verify that the booster is holding vacuum. You'll find the exact measurement in the FSM for what it's supposed to hold. You want to check 4 clamps (1 where the hose goes to the booster, 2 at the check valve that is inline most likely about 4-8" away from the booster, and 1 at the other end of the hose where it connects to the intake manifold.

Master cylinder: Verify no leaks at all lines going to the master cylinder and at all brake line joint locations. Check fluid to verify there isn't any debris in it (I.E. torn seal particles), Check for fluid/missing paint around where master cylinder bolts to firewall, check for fluid/missing paint inside of the vehicle where master cylinder comes through firewall. If all of these checks look good, lets bleed the brakes to verify no air in the line. Start farthest away from the master cylinder and work closer. Passenger side rear, drivers side rear, passenger side front, drivers front. When you bleed the brakes, if you're not able to build up pressure after its done...then you have a bad master cylinder.

Doing these tests will set you back about $7 for brake fluid and you can find a vacuum pump for maybe $15. $22 is a hell of a lot cheaper than $180 and you'll know what is actually going on.

Now, if everything checks out and this was just an isolated incident then I would tend to believe that the brakes were overheated due to excessive braking. This is a whole different story, but could account for why the pedal lost pressure 1 time. With brake fade you'd be looking for glazed pads and hot spots on the rotors.

Keep us posted on how things turn out and good luck!

[EdBwoy]

Larz, I don't think it's wrong to look at things that way really. I prefer to diagnose before replacement, as offered above.

Unfortunately proper diagnosis takes time and someone's skill/ knowledge and sometimes money. If I have the knowledge to diagnose, then I'll spend some time to get to the root of the problem myself.
If I have neither time nor skill, then I'll pay someone who has some skill/ tools and time to do it for me... then they give me their best guess of the problem based on their diagnosis and I either pay them to fix it or I do it myself.

OP, I wouldn't buy those parts yet, no matter how cheap, until I've gotten a positive ID on what's wrong. The booster can be tested fairly simply without taking too much apart. The master cylinder can also be tested fairly easily, and if your knowledge of the history of the car makes you bleed the brakes, just consider that maintenance.


One advantage of using a dealer is getting a loaner while they monkey around with these possibilities.