2012 Mazda CX-9 brakes problems: brake power boost unit failure

Brake Power Boost Unit Failure

2012 Mazda CX-9

This problem may be covered under warranty. Ask your Mazda dealer.


pretty bad
Typical Repair Cost:
Average Mileage:
58,605 miles
Total Complaints:
20 complaints

Most Common Solutions:

  1. not sure (9 reports)
  2. replaced by dealership (9 reports)
  3. replace brake booster (2 reports)
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2012 Mazda CX-9 brakes problems

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2012 Mazda CX-9 Owner Comments

problem #20

Oct 162017

CX-9 Touring V-6

  • Automatic transmission
  • 72,000 miles


My wife has been a faithful Mazda person for years. But after this vehicle, if she wants to buy another I will wholeheartedly disagree. The brakes were first serviced at 30,000 miles. It needed new rotors. When I asked the shop doing the work about why I would need new rotors already at 30 k miles, (they were worn AND warped,) I was informed that the rotors were basically "throw away" rotors of poor quality from the manufacturer. Anyway, paid for the brake pads and new rotors which significantly raised the repair cost.

Now, a couple years later, and the throttle body has gone out on the engine, (see other complaint,) and the brake system has failed. The master cylinder was empty of brake fluid then my wife let me know she was having a problem with her brakes. I took it to a shop where they said they saw no leak and replaced the brake fluid. Now two days later the brakes go all the way to the floor and there is a very loud strange noise in the dash. (Power booster?) Have not contacted dealer yet but I am curious since this is now 2017 if they will honor a repair of this known issue. I will update when I know what the dealer says.

Update from Nov 1, 2017: OK. So my wife bought this vehicle with pretty low miles on it. Soon after, transmission switch failure. Replaced by dealer. I believe it failed again and had to be replaced. After that, throttle body failed at around 70 K miles.(This was after the vehicle would stall upon kicking in the passing gear to merge onto the highway.) It would cause a sputter and shudder and shutdown. Pretty scary stuff. Luckily I was able to pull off into the breakdown lane. This happened multiple times with multiple trips to the dealer. (They could not diagnose because of no codes. Told them to ride with me and I could show them!) So, the throttle body is not warrantied. It acts like a governor so as long as you don't floor it it's fine.

Now the latest update. Taking it in for the BRAKES issue. This is a 2012 but Mazda extended the warranty on the booster because it was a known issue I am sure. Called dealer. No towing paid for for repair. Said "Most people just drive them in." Really? The pedal goes to the floor and it makes a hellacious noise in the dash. Seems same problem as reported to me. I towed and paid out of pocket to get it there because it was unsafe to drive imo. Anyway, Master Cylinder failed, (this is at 75K miles btw,) and Mazda said it was not covered! But, the booster was! (And the replacement for safety recall airbag.) I used to run a shop. I said "OK Please do the free airbag recall and the power booster. I will then take it to a shop of my own to fix." Tech said "Well, we cannot install the power booster and put the master cylinder back on because it would fail again." I explained to Josh that I had run shops before and that I know what I am doing. Asked him to just leave the MC off and I would tow it. Said he would have someone call Mazda. Told him my wife has been a faithful Mazda enthusiast and that this is ridiculous. Waiting to hear more.

- , Indianapolis, US

problem #19

Aug 122017


  • Automatic transmission
  • 80,000 miles

Heard the hissing for a week, got a little concerned and was lucky not to be driving close to others when the brakes didn't stop the vehicle as expected. Has this caused anyone to rear end another vehicle yet?

- , South Riding, US

problem #18

Jul 162017


  • Automatic transmission
  • 48,000 miles

Purchased the CX9 in June 2017. the car was having problems braking and it would shut off at a red light. Took it back to dealer and they said it was a vacuum leak and brake booster. Car is still under warranty so the dealer is fixing it. Mazda should have an official recall for this problem.

- , Quincy, US

problem #17

Apr 042017

CX-9 Grand Touring

  • Automatic transmission
  • 40,300 miles


A serious safety issue if on highway or driver isn't strong enough to compensate for the loss of assisted braking.

- , Plano, US

problem #16

May 012017

CX-9 V6- 3.7L

  • Automatic transmission
  • 83,245 miles

One day it was fine the next it was hard to brake, spongy pedal and hissing noise same as everyone else. I took it in to a regular service shop to see what was wrong. I need front bakes and a new booster. Estimate $2000! So I decided to look online and found Mazda extended warranty. I have an appointment tomorrow and they said I can have a rental while waiting for part to arrive. This is such a dangerous situation. Why is this not on the recall list!! The 2012 model is not even on the original list of affected models. Only after calling the dealer did I find out it was included. I am 7000 miles under the limit...thank goodness! What else should I be looking at before time is up?!!!

- , Napa, US

problem #15

Oct 172016

CX-9 Touring AWD 3.7L V6

  • Automatic transmission
  • 52,500 miles

Brake booster failure with the same symptoms as described by others on this site (e.g. increased stopping distance, soft/spongy brake pedal, hissing noise). I am on my second pair of front brake pads while the rear pads are still original. All brake service on the car has been performed at the dealer). While I'm glad that Mazda has paid enough attention to this particular issue to extend the warranty (7yrs/90K miles) and provide replacement coverage, this is a serious safety problem. Prior to repair, my ability to stop the car was greatly reduced. If it hasn't already occurred, somebody is going to have an accident due to this problem. Given the critical nature of both the system and involved and the type of failure that many appear to have experienced, a recall is warranted.

On a related note, this is the 3rd significant warranty repair for this vehicle. The other two were; 1) moonroof leaking @ 30K miles, and 2) transfer case leaking/failing @ 40K miles. The transfer case in particular is problematic--even the Mazda Service desk indicated that the replacement will eventually fail prematurely, "It's the Achilles of the vehicle", he said. That's a $2K+ problem outside of warranty. Prior to this, I've only owned Honda and never experienced any type of significant repair issue beyond normal wear and tear. The CX9 is a great car but I am disappointed at the number of basic mechanical failures. For this reason (and regrettably), I am disinclined to purchase another Mazda in the future.

- , Lansdale, PA, USA

problem #14

Feb 102017

CX-9 V6

  • Automatic transmission
  • 75,000 miles


The Booster gave out at the wrong time, which a truck almost hit me and I couldn't even stop and with 3 kids in the car. It was the worst feeling and how upsetting it was. My car is going into the shop on 2/14/17 and I feel this should have been address sooner.... I think of what could of happen and I would of sue Madza for everything. My kids were in the car at the time and I thank god that I was able to come to a very close stop. My kids are my life and I put my trust that I had a safe car and I don't think I do anymore...

- , Powell, TN, USA

problem #13

Nov 222016

CX-9 Touring FWD 3.7L V6

  • Automatic transmission
  • 58,500 miles

Drove ~600 miles with a failed brake booster. Found out via internet that Mazda had provided an extended warranty to cover this defect. When the dealership where I took the car tried to find the part it was on backorder with Mazda. The Mazda service manager at Preston Mazda, John Rosensteel, had one of his people drive to Butler, PA from Boardman, OH to pick up the part. I took the car to the dealer on the day before Thanksgiving and the car was ready to go with a new boost unit by Friday. This was all due to the efforts of an excellent service manager at the dealership. Mazda failed me as a customer by not having the brake booster in stock even though it was the subject of multiple failures and an extended warranty.

- , Greer, SC, USA

problem #12

Nov 212016

CX-9 Touring 3.2L V6

  • Automatic transmission
  • 140,000 miles

I knew there was a problem when I was in a drive thru and when I pressed my brakes instead of stopping I almost ran into the person in front of me. Then I started hearing the hissing sound whenever I stepped on the breaks. At first I thought I needed my brakes replaced so I went to a brake repair shop and was told it was in fact my booster and it would cost roughly $1200. Then I went to another shop and they offered to replace the booster for $600. Finally I called the Mazda dealership to see if this booster would be covered under my warranty. After they verified my vehicle they informed me that, yes, I did have the extended warranty but it was for 7 years or 90,000 miles which ever came first. Unfortunately my vehicle already had 140,000 miles so they told me it was not covered and it would cost $800 before taxes.

With all this happening around the holidays it was just too much. Since my car is only 4 years a old a friend suggested I call the Mazda headquarters and complain since many others are having the same problem. After I called Mazda headquarters they told me to take it back to the dealership so that it could be diagnosed as a booster problem and they would in fact honor my extended warranty. I am pleased to say that after I took it back they diagnosed the booster as being bad and they did honor my warranty. If you are having this same problem please contact Mazda headquarters so you can report the problem and have them fix it for free. After having my vehicle repaired it is running perfectly fine and I am no longer stressed about having my family in an unsafe vehicle.

- , Temple, TX, USA

problem #11

Aug 262016

CX-9 Touring 3.7L V6

  • Automatic transmission
  • 52,000 miles

After a one-month of being gone out of the country when I came back I took the car for a drive and I realize that all the sudden my brake pedal was very hard and as I was pushing the brake pedal it wasn't stopping the car and I could keep hearing a hissing noise and I panic

Checked on the internet and I seen there is a familiar problem with this model and year of CX9of and I took it to the dealer still hoping that it ll be coverd by the warranty, and they told me that is an extended warranty for it and they fixed it; otherwise this car is a very good car overall and I'm very happy with it this was a great surprise to me about the brakes and I'm definitely blessed not to get myself into a terrible accident

- , Hoffman Estates, IL, USA

problem #10

Aug 222016

CX-9 Touring

  • Automatic transmission
  • 101,000 miles


Weeks after taking car to dealership for a recall order on a separate issue, we noticed that brake pedal became increasingly "spongy." (Odd, since dealership inspection showed no brake issues... ) Loss of brake fluids soon followed as well as inability to stop the car in bumper to bumper traffic -- even when brake pedal was pushed to floor. Hissing noise could be heard when trying to use brakes. Called dealership and was told that we weren't covered for free brake booster "fix" since we were over mileage cutoff. Luckily, non one was injured or killed..

- , Beaufort, SC, USA

problem #9

Jul 122016


  • Automatic transmission
  • 57,000 miles

This issue came out of nowhere. I was driving with the cruise control engaged and came upon traffic. When I attempted to apply the brake it was hard to depress. I then applied greater pressure to the pedal and it was as if the I broke through a barrier in the brake system and I then slammed on the brake cause the tires to screech. Now every time that I apply the brakes it is difficult to press and there is a hissing sound. Also after the initial resistance the pedal because spongy causing the car to then stop more abruptly.

- , Moseley, VA, USA

problem #8

May 072016

CX-9 Touring V6

  • Automatic transmission
  • 43,000 miles

Car was fine on Friday.... The next day no power brakes.. Just a soft hissing sound when you push down on the pedal.. I will be contacting Mazda on Monday.. I am very upset to see that this is a common problem from what I have read on the internet..

Update from May 11, 2016: Update... Called my local Mazda dealer on Monday and they took the car in on Tuesday and fixed the problem free of charge.. Very happy with the service I received. I just wish that Mazda would have sent out a recall notice so that we could have taken care of the issue before it happened.

- , Greensburg, PA, USA

problem #7

Apr 152016

CX-9 3.7L

  • Automatic transmission
  • 60,000 miles

Progressively worse. My 1st Mazda. At first I thought it was something I needed to accept but it now lurches forward at times when I was already at a stop.I have started putting it in Neutral at stops. Weird whining noise if you continue to push down on pedal.

- , Columbia, SC, USA

problem #6

May 062016


  • Automatic transmission
  • 62,133 miles

The brakes have become very hard when trying to apply for a stop. It feels like car is now going to stop in time, I had to switch to Manual Transmission (luckily car has this feature) in order to get home, using down shifting technique. Very Scary.

- , Long Beach, NY, USA

problem #5

Mar 152016


  • Automatic transmission
  • 41,680 miles

The brakes have become very difficult to push. They slow down the car, but require intense pressure to bring the vehicle to a complete stop. There is also a slight hissing noise when the brakes are applied. It takes about twice the distance to come to a complete stop than previously. There is no indication of a problem on the dashboard; no warning light has been displaying, but something is definitely wrong. I do not feel very safe when driving.

- , Erda, UT, USA

problem #4

Feb 222016

CX-9 Touring 3.7L V6

  • Automatic transmission
  • 19,263 miles

This brake problem has apparently already been identified and resolved for 2010 - 2011 Mazda CX9 - see the following link: [http://www.mazdaproblems.com/trends/hissing-brakes/], but there was no mention of my model year (2012). I discovered this information, on your website, before I went to the Mazda dealer in Edmonton about the brake problem.

Symptoms of the brake problem included: loss of power assist making the brakes really hard to push at times: and, hissing noise coming from behind the dashboard area. The problem with my car started about 2 or 3 weeks before going to the dealership and the "hard pedal" was only occurring during very slow speed parking maneuvers. I printed out the information from the web page, showed the dealer, on March 11, 2016, and explained that my brake problem was exactly as described on your website.

The service people at the dealership told me that they had never heard of this problem and were skeptical that I had accurately diagnosed the problem by simply reading about it on your website. The dealer checked the car and confirmed brake booster failure is the problem, and told me that the car is unsafe to drive. The replacement part has to be shipped from Vancouver BC and I have an appointment on Tuesday March 15th for the work to be done.

I have a concern that, according to the information I read on your website the NHTSA thinks this problem was limited to the 2010 and 2011 model years. Therefore NHTSA, Mazda, Mazda dealers, and 2012 CX9 owners should all be notified that the problem is occurring with 2012 models as well!

- , Edmonton, AB, Canada

problem #3

Dec 192013

CX-9 GT 3.7L

  • Automatic transmission
  • 932 miles

Mazda CX- 9 2012 model I purchased on Nov-26-2013 from show room here in Qatar. From the day I have lots complaints in my car. I am complaining about my car to the show room manger and the service engineer and they just make its a silly issues. After a week my car stuck over road several times and they took into the service that is BRAKE POWER BOOST UNIT FAILURE. This I know only after 8 months when I got the service history of my car. They replaced it without saying anything. I ask about the complaints they say just jammed. After one week my car can't start. Again I call them for assist, it took one week again to get them respond about my compliant and they replace the battery and starter.

Another problem with power window motor I can't open and close the both front windows. I inform them they said we will see in next service. After only 5000km I used my car my brake pad and disc got damaged. They say I am a rash driver, that's why brake pad damaged, I replaced it . Before another 5000km I can't use my car because disc and brake pad damaged again. I can't move my car. I ask them service history of my car, they refuse to give me because recently some of other car brands showrooms closed here in Qatar by consumer court because of violations of consumer law. I hope I will get any contact details for Mazda through here better than contact dealer here in Qatar hopefully.

**please ignore any mistakes here I make. Thank you.

- , Doha`, Qatar

problem #2

May 072015

CX-9 Grand Touring 3.7L V6

  • Automatic transmission
  • 40,550 miles

Over the course of several days, the brake pedal didn't feel normal or it required more pressure to stop the car. The problem was intermittent and I thought it might just be me. Then I was sitting in a drive-thru and the a/c kicked on or off causing the revs to rise and I lunged forward almost hitting the car ahead of me. I knew that I had a problem at that point.

After some research online, I determined that the brake booster was the most likely culprit. The following Monday, I took it to the dealership and told them what it was doing and that I felt the brake booster was the issue. The service writer explained that Mazda had extended the warranty on the brake booster beyond the basic 3-year/36k mile warranty. Since I was 4550 miles over the 36k limit, I was glad to hear that.

It took four days for them to get the part and perform the repair, but they gave me a loaner to drive. Overall, I still love the vehicle and have had no other troubles since it was new. My only concern is that Mazda hasn't performed a recall on the CX-9s affected (which would cost them a lot more) rather than simply covering the ones that fail under warranty. The potential for an accident is very high for someone when the brake booster fails, especially if the driver needs to stop very quickly or lacks the physical strength to apply a LOT of extra pressure to the brake pedal.

- , Waleska, GA, USA

problem #1

Nov 192014

CX-9 Touring 3.7L V6

  • Automatic transmission
  • 45,000 miles

Excellent car!!! No issues accept the bad Brake Power Boost Unit that was replaced under warranty. Acceleration is great, the ride is a true pleasure. Though many convenience additions are absent (e.g. power liftgate, automatic folding mirrors, memory seats, tire pressure sensors) the car is built very well. Comfortable heated front seats (both electrically powered), good noise isolation, pleasant leather upholstery, a lot of cargo space with the 3rd row folded, rear a/c, sliding 2nd row!

Love the car!

- , San Diego, Ca, USA

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