Master cylinder or brake booster failure on the 2009 Mazda CX-9
When master cylinder or brake booster failure gets reported
Owners of the 2009 Mazda CX-9 report master cylinder or brake booster failure at a median of 100,000 miles. A quarter of the reports come in before 85,000 miles and a quarter after 120,000 miles, from 8 reports that carried an odometer reading.
A part like this is normally expected to survive 92,000 miles. It is the 2nd most-reported problem on this model year.
The mileage distribution
The reported range runs from 45,000 miles at the tenth percentile to 140,000 miles at the ninetieth, a spread of 96,135 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 |
|---|---|---|---|---|
| 43,065 miles | 86,984 miles | 101,280 miles | 120,750 miles | 139,200 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
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 2009 has 8. 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 2009 mazda cx-9. The contact stated that while driving approximately 40 MPH, excessive force had to be applied to the brake pedal in order to bring the vehicle to stop. The vehicle was taken to a private mechanic where the contact was informed that there was fluid leaking from the master cylinder to the power booster. The contact was also informed that the power booster needed to be replaced. The manufacturer was not notified of the failure. The vehicle was not repaired. The approximate failure and current mileage was 38,000. *tr
So I was backing up from a parking space on a shopping center and my brake pedal on my mazda cx-9 did not stop immediately. Due to this problem I bump in to some one else's car. The pedal has turn so hard it was difficult for fractions of seconds to know what was going on. After the incident with having an issue with the brake pedal. I notice beside been hard it started making a squeaky noice and also like and air sound under the dash board. I found out there was a class action agains mazda for their brake booster on this model and sure enough, that's what it was, I'm just so blessed it happens in a parking lot and not on the freeway. So I called mazda and they said they will cover the part but I have to pay for the work done to the vehicle. So I did a research on pricing and I found out mazda is charging $269.00 for the wok done, supposedly them covering the part, and outside that is just around the same price else where. Not only that they did not cover everything most likely my insurance may go up and to add to the problem they will charge me for renting a car while they fix it. There is no help with a part that should not have…
So I was backing up from a parking space on a shopping center and my brake pedal on my mazda cx-9 did not stop immediately. Due to this problem I bump in to some one else's car. The pedal has turn so hard it was difficult for fractions of seconds to know what was going on. After the incident with having an issue with the brake pedal. I notice beside been hard it started making a squeaky noice and also like and air sound under the dash board. I found out there was a class action agains mazda for their brake booster on this model and sure enough, that's what it was, I'm just so blessed it happens in a parking lot and not on the freeway. So I called mazda and they said they will cover the part but I have to pay for the work done to the vehicle. So I did a research on pricing and I found out mazda is charging $269.00 for the wok done, supposedly them covering the part, and outside that is just around the same price else where. Not only that they did not cover everything most likely my insurance may go up and to add to the problem they will charge me for renting a car while they fix it. There is no help with a part that should not have…
Also reported on the 2009 Mazda CX-9
Airbag inflator rupture
Differential or transfer case failure
Other brake problem
Water pump failure
Tail light, brake light or signal failure
Other suspension problem
How far this goes
Complaints are voluntary, so 8 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 2009 Mazda CX-9?
Across 8 owner reports that included an odometer reading, half were filed by 100,000 miles. A quarter were filed before 85,000 miles and a quarter after 120,000 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 2009 Mazda CX-9?
8 reports have been filed with NHTSA, about 0.3 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