MajorCommonBrakes

Mazda CX-9: Brake booster diaphragm tear — hard pedal and hissing

Brake booster diaphragm tear — hard pedal and hissing is a common brakes fault on the Mazda CX-9 on the 2007–2015 cars, and we rate it major. Putting it right costs $800 to $1,600 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 26 documented faults on the Mazda CX-9.

Vehicle: Mazda CX-9
Years: 2007–2015
Fuel: petrol
System: Brakes

This page covers the Mazda CX-9 as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Mazda CX-9 faults26 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph for this fault yet. We would rather show none than show a picture of something else.

What goes wrong

The gen-1 CX-9's vacuum brake booster diaphragm develops tears near its outer seal (a manufacturing mould-wear defect, worse in hot climates). The pedal becomes hard to press with much-reduced assistance, and a hissing noise appears from the driver's footwell when braking. NHTSA investigated 2010-2011 models and Mazda extended the warranty on 2007-2013 cars to 7 years/145,000 km — that coverage has long expired, so any surviving car with an original booster is on borrowed time. It never became a formal recall.

What you would notice

Brake pedal suddenly very hard to press
Hissing from behind the pedal when braking
Longer stopping distances
Symptoms may be intermittent at first

How to check it

Where to look. Brake booster on the firewall behind the brake pedal, driver's side engine bay

With the engine off, pump the pedal several times, hold pressure, then start the engine — the pedal should sink noticeably (booster working). During the test drive listen for hissing under the dash when braking and note pedal effort. Ask for evidence the booster has already been replaced.

What it costs to put right

$800 to $1,600 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has the brake booster ever been replaced?”
“Is there any hissing under the dash when you brake?”

Now check the Mazda CX-9 you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

Australian Car Reviews 'Recalls & faults: Mazda TB CX-9 (2007-15)' (diaphragm tear root cause)
MazdaProblems.com 'Spongy CX-9 pedals because of brake booster failure'
CarComplaints 2012 CX-9 brake power boost unit failure (27 complaints) and 2014 NHTSA investigation coverage
Mazda 2007-2013 CX-9 brake booster warranty extension (7yr/90,000mi, ended March 2015)

Mazda CX-9 buyer questions

Is brake booster diaphragm tear — hard pedal and hissing serious on a Mazda CX-9?

We rate it major and common on the Mazda CX-9. The gen-1 CX-9's vacuum brake booster diaphragm develops tears near its outer seal (a manufacturing mould-wear defect, worse in hot climates). The pedal becomes hard to press with much-reduced assistance, and a hissing noise appears from the driver's footwell when braking. NHTSA investigated 2010-2011 models and Mazda extended the warranty on 2007-2013 cars to 7 years/145,000 km — that coverage has long expired, so any surviving car with an original booster is on borrowed time. It never became a formal recall.

How much does it cost to fix on a Mazda CX-9?

$800 to $1,600 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Mazda CX-9 years are affected?

Our research records this fault on the 2007–2015 Mazda CX-9. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.