Master cylinder or brake booster failure on the 2008 Mazda CX-9
2 crashes 1 injury 3 of the 13 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 2008 Mazda CX-9 report master cylinder or brake booster failure at a median of 70,000 miles. A quarter of the reports come in before 40,000 miles and a quarter after 100,000 miles, from 11 reports that carried an odometer reading.
A part like this is normally expected to survive 92,000 miles. It is the 6th most-reported problem on this model year.
The mileage distribution
The reported range runs from 15,000 miles at the tenth percentile to 155,000 miles at the ninetieth, a spread of 142,800 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.
18% of the dated reports were filed under 36,000 miles.
The whole distribution
| 10th | 25th | Median | 75th | 90th |
|---|---|---|---|---|
| 13,200 miles | 38,583 miles | 68,000 miles | 101,000 miles | 156,000 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, 2 a crash and 1 an injury are 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 2008 has 13. 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 2008 mazda cx9. The contact stated that while driving approximately 20 MPH, the brake warning indicator illuminated on the instrument panel. The indicator remained illuminated until the engine was turned off. The failure had not been diagnosed or repaired. The manufacturer was not made aware of the failure. The contact stated that the defect could possibly be contributed to an internal brake fluid leak. Currently, there was an open investigation under NHTSA action number pe11026 (service brakes, hydraulic:foundation components:master cylinder). The approximate failure mileage was 46,000.
Tl* the contact owns a 2008 mazda cx-9. The contact was driving 20 MPH when the brakes were depressed and the vehicle failed to stop properly, and crashed into a gate. The crash caused no injuries and the police were not contacted. The same failure recurred on multiple separate occasions and without warning. The vehicle was taken to the dealer where the dealer confirmed that both the master cylinder and power booster were leaking brake fluid and needed to be replaced. The manufacturer was contacted. The vehicle was repaired. The failure mileage was 68,000 and the current mileage was 68,200. Updated 04/26/12*lj according to the repair invoice, the brake booster was leaking due to corrosion from brake fluid leaking from the master cylinder into the booster. The brake master cylinder and booster were replaced. Updated 04/27/12
Tl* the contact owns a 2008 mazda cx-9. The contact was driving 20 MPH when the brakes were depressed and the vehicle failed to stop properly, and crashed into a gate. The crash caused no injuries and the police were not contacted. The same failure recurred on multiple separate occasions and without warning. The vehicle was taken to the dealer where the dealer confirmed that both the master cylinder and power booster were leaking brake fluid and needed to be replaced. The manufacturer was contacted. The vehicle was repaired. The failure mileage was 68,000 and the current mileage was 68,200. Updated 04/26/12*lj according to the repair invoice, the brake booster was leaking due to corrosion from brake fluid leaking from the master cylinder into the booster. The brake master cylinder and booster were replaced. Updated 04/27/12
Also reported on the 2008 Mazda CX-9
Control arm, ball joint or bushing failure
Other suspension problem
Airbag inflator rupture
CV axle or driveshaft failure
Differential or transfer case failure
Other brake problem
How far this goes
Complaints are voluntary, so 13 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 2008 Mazda CX-9?
Across 11 owner reports that included an odometer reading, half were filed by 70,000 miles. A quarter were filed before 40,000 miles and a quarter after 100,000 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 2008 Mazda CX-9?
13 reports have been filed with NHTSA, about 0.5 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