DarkBlue555

2006 Cayenne S

All,

I have been going nuts trying to fix my soft brake pedal. The pedal is firm with the engine off, then becomes soft/squishy once the car is started. I can easily push it down to the ‘hard stop’ point. The brakes do work, but it requires pressing the pedal nearly to the floor. No brake fluid is leaking. The dealer says they don’t know.

What I have tried so far:

New OEM pads and rotors
New master cylinder
Installed stainless brake lines
EXTENSIVE Brake Bleeding (using Power Bleeder)
Yelling at the car

I’m curious if the brake booster can cause this, since I have read conflicting reports. My understanding is that a failed booster will cause the pedal to stiffen, which is not what I’m experiencing.

I am willing to replace the booster if that is the issue, but I would like to hear feedback from others.

I do not have any warnings lights on.

My alternate theory is air in the ABS module, but I don’t think the first generation cayennes require circulating the pump, so the air should be purged by normal bleeding.

I am open to any and all theories.

hopsis

Master cylinder maybe?

celiawessen

Pelican Parts has a detailed article about troubleshooting the 955 brake system.

https://www.pelicanparts.com/techart...r_Problems.htm

DarkBlue555

Already replaced it.

DarkBlue555

Thanks for the link. The following quote from the article makes me think the booster could be the problem:

“You'll want to check if the brake pedal goes to the floor with the engine off. If it doesn't, you have a problem with the system.”

Very interesting.

Petza914

Those are textbook failed master cylinder symptoms. Was it a quality part from a reputable seller or an ebay or Amazon one you installed. Is there much braking power at all even though the pedal is low. You can bleed the abs circuit by finding a construction side where trucks pulling in and out have left a light coating of dirt in the road like in a neighborhood where they're building a house and then locking up the brakes on it a few times.

dchown

Yes! I have the exact same issue. I have power bled the brakes thoroughly and replaced pads/discs. No signs of leaks and booster seems to generate plenty of force (is easy enough to push pedal to the floor), and if I come back hours later there is plenty of residual vacuum in the booster. ABS activates on snow no problem but not on dry pavement (brake pressure can't always overcome the grip).

Did you ever resolve this? Any info would be much appreciated.

Dan

'04 Cayenne Turbo

Petza914

You can purge the abs system by engaging abs, then doing some regular bleeding at the calipers. Find some dirt on the road like near where they're building a house and do some hard stops to engage the abs, the bleed again at home.

JoelSV

I have this exact same issue on my 2006 Cayenne S. Any update on how you resolved it?

Thanks!

phatz

Interesting that they are zero day accounts and then vapor

touareg

I will update when I find out, same problem on my 09. Just flushed and replaced fluid as the car has been mostly sitting during covid.

mbardeen

I had similar symptoms on my 957 CTT. I found a broken vacuum hose coming off the vacuum pump - fixing that fixed the soft pedal.

JD305

can you post a photo in the general area where you looked? .. I need to start looking at this problem, when coming down the ramps in my condo parking garage, it takes some braking effort to stop

Thanks!

Joefus

Hi All,

I had a similar situation 2 weeks ago on my 06 CTTS.

Changed front pads and rotors - used a power bleeder to flush out the old fluid and replace - bled all 4 callipers at both bleed nipples..

Pedal was hard when the engine was off - became soft when the engine was on.

I bedded in the brakes with some 30mph-5, 40-5, 50-5 and 60-5 runs on a quiet stretch of road.

Solution was to hook up the power bleeder with fluid in - but to make sure the brake pedal was depressed a couple of times when bleeding in the old school - non-power bleeder method.

There was obviously some air hiding in the system that was only shifted when the pedal was depressed - that the power bleeder wasn't shifting.

Pedal is rock solid now.

Hope that helps.

mbardeen

Back left of the engine.

https://www.youtube.com/shorts/oYVSHuGyWh0