Brake Power Boost Unit Failure

2012 Mazda CX-9 (Page 1 of 2)

This problem may be covered under warranty. Ask your Mazda dealer. Seal Of This Might Hurt Notes: The only area of real concern for 2012 Mazda CX-9 owners is the brake booster.

In 2014, Mazda extended the warranty on the 2007-2013 CX-9 brake booster to 7 years / 90,000 miles. However this extended warranty has expired for most CX-9 owners, so buyer beware.

This Mazda CX-9 brake booster failure isn't terrible in terms of repair cost — it "only" costs $550 average to fix. However it is a safety issue when the brake booster fails as it increases stopping distance. Owners have reported having to stomp on the brake pedal, & crashes/injuries have been reported due to this CX-9 brake booster defect.


pretty bad
Typical Repair Cost:
Average Mileage:
67,800 miles
Total Complaints:
27 complaints

Most Common Solutions:

  1. replaced by dealership (10 reports)
  2. not sure (9 reports)
  3. replace brake booster (7 reports)
  4. too soon to tell (1 reports)
2012 Mazda CX-9 brakes problems

brakes problem

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2012 Mazda CX-9 Owner Comments (Page 1 of 2)

problem #27

Oct 062020

CX-9 Touring V6

  • Automatic transmission
  • 85,896 miles


I bought this Mazda used in March 2015. Several months ago I would notice a hissing noise when I pulled into garage. Then I noticed the brake pedal seemed hard to push. Then one day when I was approaching a traffic light and started to push on brake pedal it was not stopping. I started pushing harder and pumping and it eventually stopped. I googled "brake problems with Mazda CX9" and discovered this problem was not unusual. I took it to the local Mazda dealership and had the Brake Booster Vacuum replaced. It cost me $567 and I was told it was not under warranty.

I sent a letter to Mazda Customer service and the reply I received was that a letter went out in 2014 informing owners that there may be a problem. Even though I only have 85,000 miles on it it was beyond the 7 yr extended warranty so I was not reimbursed.

- Pat S., Portage, US

problem #26

Jul 062019

CX-9 Touring V6

  • Automatic transmission
  • 129,000 miles

Bought car used in 2013 and never received manufacturers letter to owners about booster failure and extension of warranty. Even though booster failure doesn't result in loss of braking, it does extend the braking distance significantly and if you're not ready for it, definitely could cause an accident. Someone who doesn't have strong legs would be in trouble. irresponsible of the manufacturer not to call this a safety recall. Booster just failed in our car at 129000 well over the extended warranty. dealer charging $980.00 including 129.00 diagnoses to fix it. They claim its a labor intensive process.

- Robert D., Milford, US

problem #25

Jun 212018

CX-9 Touring 3.7L

  • Automatic transmission
  • 115,000 miles

I was driving to go pick up lunch from work and went to stop at at light, the brake was suddenly really hard and the car seemed to not stop. I pushed the brake pedal as hard as I could and narrowly missed the stopped vehicle in front of me. I drove slowly back to work and looked up what could be the cause. I then found all the complaints and the exact same situation I found myself in.

This needs to be recalled and all units need to be replaced before something bad happens!

I called Mazda and learned about the extended warranty which I was never notified of. But since I was a little past the mileage they offered for me to bring it to the dealership and pay the $100 diagnostic fee and they "might" cover it under the warranty due to the years. The part is only $106 from the dealership.

I will just get it replaced and save my receipts for when it gets recalled.

- Amanda G., Canton, GA, US

problem #24

Aug 312018

CX-9 Touring V6

  • Automatic transmission
  • 120,000 miles


Hissing from brakes and have to push really hard to get vehicle to stop.

- Kenneth C., reisterstown, MD, US

problem #23

Aug 012018


  • Automatic transmission
  • 101,500 miles

CX-9 Brakes not stopping car in a safe manner. Drivable but need to be cautious in city areas to stop in time. CX-9 being bounced around shop to shop. Brake Booster and Master Cylinder replaced at approx. 77,000 mile. Booster replaced at a Local Shop under and after market warranty, Master Cylinder replaced at Madza Dealership under a Service advisory/extended warranty. CX-9 now has a new set of rear pads and rotors installed at Local Ford Dealership, then went to the Mazda Dealership to look at the Master Cylinder diagnosed by the Ford Dealership. Mazda Dealership indicates it is not the Master cylinder but it is the after Market Brake Booster installed in our local shop. Car drove to the local repair shop 8/15 and replaced brake booster. tested fine but the shop installs a new brake booster to satisfy us. Problem is not resolved so vehicle is going to Mazda Dealership to assess the Master Cylinder.

Update from Nov 23, 2018: CX9 at the Mazda for nearly 4 weeks ( fortunately have a loaner Vehicle 2018 CX9) . Shop called and informed we needed a ABS module and would be over $1000 for the service. After some discussion it was agreed I could source a replacement ABS module and had one shipped in for less than $200. Shop installed said ABS module was defective . I called the Used part dealer no issues they sent a replacement ABS Module to replace the first one. The 2nd ABS control module installed and the dealership replaced the Brake Booster they had installed a few thousand miles prior. I my discussion with the dealership they were not certain of the original issue with the brakes as this " is very unusual for the CX9 to experience all these brake issues and our techs have not really seen anything like this". So I negotiated a price for this work that was accomplished with no real great satisfaction or confidence i won't be dealing with the brakes again.

- David Z., Kennewick, WA, US

problem #22

Jun 102018


  • Automatic transmission
  • 58,768 miles

There was a previous investigation (NHSTA) for previous model years. Closed "vendor fixed" but there's a TSB for the same issue for 2012 (and beyond?) The dealer didn't execute a fix (claim they weren't allowed to because there were no symptoms in march). From nothing they could find to catastrophic brake failure in roughly 60 days!?!

Clearly, there is a significant design defect; it wasn't corrected. The dealer did not notify my mechanic (so I'm out of pocket AND the warranty wasn't extended). Booster failure should NOT result in total loss of braking, it should result in reduced braking effectiveness.

There should have been a recall for the 2011 problem and earlier. There should be one for 2012 and beyond. The design is clearly defective; and the parts used (there are no third party alternatives) are dubious.

- Keith B., Englewood, CO, US

problem #21

Dec 152017

CX-9 V6

  • CVT transmission
  • 47,467 miles


I was in front of my daughter's school pulling up to the curb when it happened. I tried to brake and was having trouble applying the brake. It was real hard. I had to use both feet to apply pressure. When I did so, the car then shut off. I was shaken up and not sure what had just happened. I went to leave the school and luckily its 10mph in the parking area. I tried to brake again and realized this was impossible. I ended up parking the car in a gas station and waited for a tow truck to come and get us.

While we waited for over an hour I was Googling what happened. The sounds I heard (a hissing sound) when I tried to apply the brake. The car shutting off. The feel of my foot trying to brake was all described on a master brakesman page. It stated the brake booster would be the issue. I explained this to the Mazda dealership I had my vehicle towed to.

They checked my concerns and yes it was the problem. They replaced the brake booster assembly. I inquired that my car should still be under warranty. Because we moved to Guam its not covered under the warranty they said. So I had to pay out of pocket. Yes, this is the dumbest thing I ever heard of. Guam falls under Japan Mazda dealership. There is no recall on this either.

I left with my car and unhappy with what was spent. Only to have several lights come on. The TCS, Low tire pressure and trac control and the brakes felt squishy, and acceleration fluctuated and the car had to be driven in manual from automatic. Turned around and they had to adjust the brake switch to the new booster rod and they adjusted the brake. Left again and lights came on again. The mechanic said they would order new brake booster. The one I have must be faulty.

The car has been sitting for 3 weeks and we called to find out if the part made it on island. The mechanic never ordered the part and is on vacation. He also did not put the notes in the system about the part being ordered. No part!!!!!

- Ceiba P.,

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.

- Dave A., 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?

- Andrew H., 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.

- Yvette B., 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.

- Jose T., 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?!!!

- Rebecca G., 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.

- Christopher M., Lansdale, PA, US

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...

- Gypsey Z., Powell, TN, US

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.

- Jeff H., Greer, SC, US

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.

- Shareika Y., Temple, TX, US

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

- manucrystal, Hoffman Estates, IL, US

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..

- Wendy J., Beaufort, SC, US

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.

- Zacharia C., Moseley, VA, US

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.

- James S., Greensburg, PA, US

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