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"Brake booster failure" warning light

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Old 09-04-2013, 04:16 AM
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FredR
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Default "Brake booster failure" warning light

Hi,

Do any of you wise chaps happen to know why I might have received a "brake booster failure" alarm last night? I was accelerating- presumably under some boost- when the alarm appeared. I backed off- the brakes felt just as powerful as ever and when I stopped and restarted the engine the brake pedal dipped as the engine fired.

I understand these cars have some kind of "vacuum support" sub system that automatically kicks in when under boost- presumably to ensure you have instant braking rather than some notional short delay whilst vacuum is established.

i dare something [vac line/ vac pump?] may have taken a dump- then again [hopefully?] maybe a false alarm.

Thoughts/suggestions on likely cause/solutions/costs much appreciated

Much as I know my 928 inside out I know little about this amazing vehicle as yet.

Thanks in advance

Fred R
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Old 09-04-2013, 09:29 AM
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Old 09-05-2013, 01:48 AM
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Originally Posted by bigbuzuki View Post
Thanks for the link- sounds as though that is the likely source of the problem- managed to catch my pal who is the main dealers chief mechanic- a common problem at this age it seems.

Apparently to replace that pipe altogether with a new pipe[s?] you have to remove a few more bits and pieces but nothing too drastic.
Seems Porche have not learned too much about how to spec pipes for high temp regions!

Not too comforting knowing you have a problem in the braking system. I was also advised that if you leave the old pipe in there it may eventually cause further damage to the vac pump.

If I was going to do a repair along those lines I would consider a strip of duct tape- seems a bit more resiliant.

The joys of Porsche ownership! Had to use my 928 to go to work this morning!

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Fred
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Old 09-07-2013, 05:33 AM
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The vac line was cracked and had come away from the spigot it sits on just in front of the firewall.bulkhead whatever. I am sure it could have been temporarily fixed up but once plastcis start cracking like that I suspect it is only a question of time before something else goes. Unfortunately there are two complete assemblies and [surprise surprise] you cannot purchase the component parts.

As I took the thing in this morning the car also experienced what felt like a low down misfire- the main dealers advised this is symptomatic of this failure- sounded a bit suspect to me- anyone got any comments on this?

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Old 09-07-2013, 06:50 AM
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Regarding the misfire, get them to check out your coils for cracks whilst it's in for surgery. If any are cracked, change all of them.
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Old 09-08-2013, 01:53 AM
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Originally Posted by bigbuzuki View Post
Regarding the misfire, get them to check out your coils for cracks whilst it's in for surgery. If any are cracked, change all of them.
Gdday Sport,

The coils were replaced not too long ago by the PO [a very decent Aussie chap now back down under]. No guarantees of course but she seems to be running fine once more.

The main items I kind of figure fall into the guaranteed replacement category were the coils, the Cardan shaft and the cooling pipes- two out of the three done. Doubtless there will be a raft of smaller other such items.

My first 928 snapped its drive shaft 3 months after I purchased that- ouch!

The joys of Porsche ownership. When you buy any s/h Porsche I advise folks to price the car as though you are going to spend $2.5k in the first year of ownership- assuing it is in top notch condition and previously owned by a real enthusiast, add that to the purchase price and if you do not need it consider yourself fortunate. Looked at in that perspective a factory extended warranty package does not look too bad- if you can get one- not sure what they run at these days- something in the region of $1500 for a year? Do the maths and roll the dice type of thing.

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Old 11-27-2013, 05:11 PM
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In addition to the bulkhead leak another was found by way of a smoke test done by a local garage. It seals the entire vacuum system and pumps vapor into an open port. Leaks can't hide from this test! The other leak, much smaller, was the check valve underneath the engine's torque arm which is in front of the brake booster. The bulkhead leak was massive and was plugged to discover the other much smaller leak in the check valve.
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Old 06-25-2014, 10:28 AM
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Hello
Shame on Porsche, expensive super cars built with cheap material.
Average every two months I am having new break down new defect new problem with my Cayenne
It is silly, hardly have peace of mind, every two months new story,
Yesterday "Brake booster failure" warning light comes on,
It is a common defect, it is a vacuum leak,
Crack in Vacuum hose, I fixed it with epoxy glue and tape, and then drive the car for 10 minuets the warning massage disappear
The cracked vacuum hose location on the passenger side right behind the coolant reservoir tank
Do not worry it is easy job to fix yourself.
See attached picture

[IMG]file:///A:/Car%20Service%20Manuals/Porsche/Re%20pair%20Pictures/IMG_5252.JPG[/IMG]
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Old 06-25-2014, 10:32 AM
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here are some pictures
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Old 06-25-2014, 11:17 AM
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Thanks good info. I have had that warning come on but it was due to the secondary air system blowing the fuse in the engine compartment fuse box. This happened after I pressure washed the engine bay. Didn't think I was putting to much pressure on it but something got wet and it kept blowing the fuse until a month later. I figured it finally dried out and the short was fixed.
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