Master cylinder or brake booster failure on the 2010 Mazda CX-9
1 crash 1 of the 38 reports for this failure mention a crash, a fire, an injury or a death. Those are the owner's words on the complaint form, not a verified finding, and one report can mention more than one.
When master cylinder or brake booster failure gets reported
Owners of the 2010 Mazda CX-9 report master cylinder or brake booster failure at a median of 90,000 miles. A quarter of the reports come in before 62,500 miles and a quarter after 122,500 miles, from 34 reports that carried an odometer reading.
A part like this is normally expected to survive 92,000 miles. It is the 1st most-reported problem on this model year.
The mileage distribution
The reported range runs from 45,000 miles at the tenth percentile to 142,500 miles at the ninetieth, a spread of 97,999 miles across the middle 80% of reports.
When the reports scatter this far, the mileage is telling you about how these cars were driven more than about the part itself.
0% of the dated reports were filed under 36,000 miles.
The whole distribution
| 10th | 25th | Median | 75th | 90th |
|---|---|---|---|---|
| 44,521 miles | 61,418 miles | 90,500 miles | 121,500 miles | 142,520 miles |
Read the 10th percentile as “one report in ten arrived this early”. Exact figures are shown in this table because it is the table of record; everywhere else on the site they are rounded to the precision the sample can carry.
What a percentile can and cannot tell you here
These five numbers describe the readings owners gave, in order. The median is the middle one: half the reports arrived below it. The 10th and 90th are the edges of the bulk of the distribution, and the distance between them is the part worth reading. A tight spread — say 70,000 to 95,000 miles — points at something that wears out on a schedule, and the schedule is knowable. A wide one, 20,000 to 190,000, points at a fault that hits some cars and never troubles others, which means the mileage on the listing in front of you tells you very little about your odds.
What these figures are not is a survival curve. Every reading here comes from a car whose owner filed a complaint, so the sample contains only failures: it cannot say what share of the fleet made it past 150,000 miles untouched, because those owners had nothing to report. Nor is the mileage the moment of failure — it is the odometer reading as recalled at the time of filing, which may be weeks later and is sometimes rounded to the nearest ten thousand by the person typing it.
Percentiles are shown at all only once 8 readings exist for the vehicle and mode. Below that the middle of a handful of numbers is noise wearing a decimal point, so the figures are withheld rather than dressed up.
What happens, and what it costs
Of these reports, 1 a crash is mentioned. Owners write their own complaints and the agency does not verify them, so read this as what the reports say happened rather than as a confirmed count.
Putting it right typically runs $450–$2,200 at an independent US shop. That range is an editorial estimate held in this site's failure-mode catalogue, not a figure from NHTSA, and it is a repair cost rather than a diagnosis cost.
This mode is classified as critical, which means a failure can leave the car unable to stop, steer, or stay out of the way of traffic. It is weighted accordingly in the risk score.
The same failure on other years
The same failure is reported on 7 model years of this car. It shows up earliest on the 2012, at a median of 60,000 miles, and latest on the 2009 at 100,000 miles.
By volume the 2012 carries the most reports, with 53; the 2010 has 38. A mode that appears across most years of a model is usually a design choice rather than a bad batch.
If one year stands out to the left, that is the year to avoid; if the whole line sits at a similar mileage, this is wear rather than a defect in one production run.
Tick median reported mileage Solid middle half of reports Faint 10th to 90th percentile Colour how bad the failure is when it happens
What owners wrote
Verbatim from NHTSA complaint narratives, trimmed for length. The mileage is the one the owner gave.
Tl* the contact owns a 2010 mazda cx-9. The contact stated that while driving 25 MPH, there was a delay in stopping distance once the brakes were engaged. The contact mentioned that he had to depress the brakes repeatedly in order to bring the vehicle to a complete stop. The vehicle was taken to an independent mechanic who diagnosed that the vacuum booster and master cylinder were defective and needed to be replaced. The manufacturer was not made aware of the failure. The vehicle was not repaired. The failure mileage was 50,000 and the current mileage was 50,040.
I have a 2010 mazda cx-9 with approximately 41,000 miles. I have been diligent in my maintenance-always with a mazda dealer. The car started to exhale slightly when braking. The car then did not want to brake/stop without pumping the brakes repeatedly. I was able to stop suddenly but unable to stop without ample warning at stop signs, etc. The vehicle was taken to mazda dealership where they told me that the vacuum booster and master cylinder were defective. I was not allowed to drive the car because it was not safe. They then told me the next morning that mazda/dealership found no warranty covering such a malfunction/factory defect b/c I had passed the 36,000 miles mark. I will have to pay $839 for a repair to drive my car that is an issue with the manufacturing of my car. The dealer told me I must contact mazda usa directly to see if they will pay for it-otherwise I am responsible. I have read other complaints and an article in the wall street journal both sitting the existence and experience of this malfunction. The NHTSA was said to be investigating the issue. Mazda should be forced to recall the vehicles and fix the…
Brake system failure involving master cylinder and booster. Leaking internally. Replacement cost of $1500 researched cx9 and found this problem is widespread and not being addressed.we had a minor fender bender that could have been much worse. Mazda usa has not issued any bulletins as of yet. *tr
Also reported on the 2010 Mazda CX-9
Other brake problem
Water pump failure
Differential or transfer case failure
Loss of braking
Other engine problem
Other suspension problem
How far this goes
Complaints are voluntary, so 38 is a floor and not a count of affected cars. Mileages are typed in by owners and cluster on round numbers. And the mode itself is assigned by software reading the complaint text, which is reliable in bulk and fallible one report at a time.
Questions this page answers
At what mileage does master cylinder or brake booster failure happen on the 2010 Mazda CX-9?
Across 34 owner reports that included an odometer reading, half were filed by 90,000 miles. A quarter were filed before 62,500 miles and a quarter after 122,500 miles. These are the mileages owners reported when they complained, not a prediction for any individual car.
How common is master cylinder or brake booster failure on the 2010 Mazda CX-9?
38 reports have been filed with NHTSA, about 1.6 per 1,000 vehicles. Complaints are voluntary, so this is a floor rather than a count of affected cars.
What this is and is not. These are the mileages at which owners chose to complain to a federal agency, which is not the same as the mileage at which the part fails on every car. It skews toward failures that happened outside warranty, cost real money, or frightened someone. It is still the only public dataset that carries failure mileage at all, and the shape of a few hundred readings is informative even when a single one is not. Methodology · JSON · this failure on other cars
Source Owner complaints and recall records published by the US National Highway Traffic Safety Administration, model years 1996–2027 Figures rebuilt Published by AtWhatMileage How every figure is computed