Spongy CX-9 Pedals Because of Brake Booster Failure

CX-9 owners are worried about increased stopping distances with brake pedals that feel spongy (and unsafe) or really hard to push (and unsafe). I bet you're sensing a theme here. NHTSA was looking at the issue but closed their investigation after Mazda extended their warranty.

There is no more important safety feature in your car than the brakes. Yes, teenage drivers – that’s even more important than bluetooth connectivity. Unfortunately, owners of the 2010-2011 CX-9 have been having problems bringing their car to a stop.

The Brake Symptoms

CX-9 owners, especially those in hotter climates, have been telling harrowing tales of brake problems centered around:

  • A possible loss of power assist making the brakes really hard to push at times
  • A sudden loss of braking ability with super spongy pedals
  • A strange, hissing noise coming from the pedal area

All signs pointed to a faulty brake booster, prompting a government investigation in February, 2014.

The Brake Investigation

The National Highway Traffic Safety Administration (NHTSA) centered their investigation on 62,000 model year 2010-2011 CX-9 vehicles. Sure enough, those cars were experiencing brake issues but before the investigation could continue, Mazda announced their had identified the problem.

Mazda narrowed the problem to a materials issue in the brake booster, specifically:

  • The brake booster diaphragms develop tears near the outer seal that can result in noise and degraded performance as the tears grow
  • The tears allow leakage “from the ambient to the vacuum sides of the diaphragm” which reduces the differential pressure and produces a hissing noise after the tears “reach 10-12mm in length”.
  • The problem was caused but a wear of the mold used during the diaphragm forming process.
  • Because of the manufacturing defect, high temperatures could accelerate the hardening of the diaphragm, further increasing stress on the area and leading to those tears

Additionally, Mazda found that drivers were having a hard time pushing the pedal during “initial pedal application”, but that effort diminished as the pedal was pressed further and the tear is partially sealed by the outer wall of the booster. This sudden change explains why some drivers felt the pedal turned “spongy.”

Mazda decided to extend their warranty (details below) which satisfied NHTSA, who closed their investigation in July, 2014.

The Extended Brake Warranty

Calling it a “special service program”, Mazda agreed to extend the warranty coverage for this brake issue into two separate actions:

  • For repairs done between 03/31/2014 and 03/31/2015: warranty coverage will be extended for an unlimited time and mileage for owners who receive brake repairs in this time period
  • For repairs done after 03/31/2015: owners will receive an extended warranty if 7 years or 90,000 miles

Clearly, if you’re having brake problems you’ll want to get them fixed before the end of March, 2015. Call Mazda at 800-222-5500 with any questions.

Mazda brake image via Mr. TinDC on Flickr

Vehicles That Might Have This Problem

Model Generation Years PainRank
CX-9 1st Gen 2007–2015 7.41

Story Timeline

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OK, Now What?

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