Problems with the high pressure hydraulic system.
11-20-2005, 10:34 AM
#1
Racer
Thread Starter
Problems with the high pressure hydraulic system.
Hi,
about six weeks ago the pressure to the hydraulic brake system wouldn't build up. Turned out to be a blown fuse, #15, a 40 A fuse for the hydraulic booster pump.
see this thread: https://rennlist.com/forums/964-forum/230883-thank-you-again-rennlist-saved-me.html
I replaced it and until two days ago, friday, everything was fine.
I got stuck in traffic and after some time the the PDAS warning and the brake pressure warning lights got lit along with that dreaded warning horn.
Fortunately I was only a couple of miles from home and was just outside my garage by the time all the pressure was gone and my brake pedal was rock hard.
I checked and fuse #15 was blown again...
I had to use the car yesterday so I started the engine, it took some time to get the appropriate pressure but finally all the warning lights went out.
When I got to the end of my journey I got the PDAS and the brake pressure warning together with the warning horn.
I replaced fuse #15 before I home.
Same story close to home I got the same warning lights and a rock hard brake pedal...
Replaced the fuse and let the car rest overnight.
Today, with a fresh fuse, I started the engine, the lights went out before the warning horn chimed and I drove for about 20 miles, filled up with gas, checked the fuse which was OK.
I drove home with no drama at all, checked the fuse, turned out to be OK.
I know that blown fuses are a symptom that something isn't right, but where do I start troubleshooting?
There is a relay, R51, for the brake booster pump, how do I check that the relay isn't faulty?
After doing some reading, in Adrian's book and here on Rennlist, I also suspect the hydraulic pressure switch.
Is there a way to check that the hydraulic pressure switch is operational?
There are no visual brake fluid leaks and I have checked the brake fluid levels and they are OK.
Any help appreciated.
about six weeks ago the pressure to the hydraulic brake system wouldn't build up. Turned out to be a blown fuse, #15, a 40 A fuse for the hydraulic booster pump.
see this thread: https://rennlist.com/forums/964-forum/230883-thank-you-again-rennlist-saved-me.html
I replaced it and until two days ago, friday, everything was fine.
I got stuck in traffic and after some time the the PDAS warning and the brake pressure warning lights got lit along with that dreaded warning horn.
Fortunately I was only a couple of miles from home and was just outside my garage by the time all the pressure was gone and my brake pedal was rock hard.
I checked and fuse #15 was blown again...
I had to use the car yesterday so I started the engine, it took some time to get the appropriate pressure but finally all the warning lights went out.
When I got to the end of my journey I got the PDAS and the brake pressure warning together with the warning horn.
I replaced fuse #15 before I home.
Same story close to home I got the same warning lights and a rock hard brake pedal...
Replaced the fuse and let the car rest overnight.
Today, with a fresh fuse, I started the engine, the lights went out before the warning horn chimed and I drove for about 20 miles, filled up with gas, checked the fuse which was OK.
I drove home with no drama at all, checked the fuse, turned out to be OK.
I know that blown fuses are a symptom that something isn't right, but where do I start troubleshooting?
There is a relay, R51, for the brake booster pump, how do I check that the relay isn't faulty?
After doing some reading, in Adrian's book and here on Rennlist, I also suspect the hydraulic pressure switch.
Is there a way to check that the hydraulic pressure switch is operational?
There are no visual brake fluid leaks and I have checked the brake fluid levels and they are OK.
Any help appreciated.
11-20-2005, 01:14 PM
#2
Nordschleife Master
Hiya Millemiglia
The fuse is 40 Amp , the switch should not need over 40 amp , I would guess that the switch is low amps .
The motor for the pump would be 12 volt high amp , I could see that it would need near 40 amp .
So I guess that the fuse is blowing cause the motor or the wires going to the motor have a problem .
"Is there a way to check that the hydraulic pressure switch is operational?"
Your switch is working cause it switches on the pump and then switches it off .
"There is a relay, R51, for the brake booster pump, how do I check that the relay isn't faulty?"
If you can replace it , thats one way , if you can pull it open and have a looksee , thats another way .
If you know someone with the same car , use the other cars relay for a test . Do not put a bad part in your friends car . No need to crash his car .
Everyone , I would like to do a survey on how the hydraulic system works in many C4s , to hopefully set up some sort of base lines .
Anyone care to help me set up a survey ?
The fuse is 40 Amp , the switch should not need over 40 amp , I would guess that the switch is low amps .
The motor for the pump would be 12 volt high amp , I could see that it would need near 40 amp .
So I guess that the fuse is blowing cause the motor or the wires going to the motor have a problem .
"Is there a way to check that the hydraulic pressure switch is operational?"
Your switch is working cause it switches on the pump and then switches it off .
"There is a relay, R51, for the brake booster pump, how do I check that the relay isn't faulty?"
If you can replace it , thats one way , if you can pull it open and have a looksee , thats another way .
If you know someone with the same car , use the other cars relay for a test . Do not put a bad part in your friends car . No need to crash his car .
Everyone , I would like to do a survey on how the hydraulic system works in many C4s , to hopefully set up some sort of base lines .
Anyone care to help me set up a survey ?
11-21-2005, 07:05 AM
#3
Racer
Thread Starter
Update:
I've had no problems with blown fuses since yesterday.
We've got the first snow for the winter so I've got a lot of opportunities to test that both PDAS and ABS is working (and great fun it was...).
I also tested the traction control program, works fine.
When I started the car this morning, the PDAS warning and the brake pressure warning light showed for about 20 sec and then disappeared.
No warning "buzzer".
I hate these intermittent faults!
Any ideas of what may be causing this are highly appreciated.
I've had no problems with blown fuses since yesterday.
We've got the first snow for the winter so I've got a lot of opportunities to test that both PDAS and ABS is working (and great fun it was...).
I also tested the traction control program, works fine.
When I started the car this morning, the PDAS warning and the brake pressure warning light showed for about 20 sec and then disappeared.
No warning "buzzer".
I hate these intermittent faults!
Any ideas of what may be causing this are highly appreciated.
11-23-2005, 12:36 PM
#4
RL Community Team
Rennlist Member
Rennlist Member
Hey Peter - have you removed all of your ground points in the front trunk, cleaned them (wire brush or similar) then reinstalled them? The ground points are usually something like a 10mm bolt to the body sheet metal with wires going to them. I think there are 3 or so of them in the front trunk in various locations.
If the motor is running correctly, but intermittently blows a fuse, then a poor ground could be a source of the fuse blowing. If you have not yet checked all the ground points, this is a must do when tracking down electrical issues.
If the motor is running correctly, but intermittently blows a fuse, then a poor ground could be a source of the fuse blowing. If you have not yet checked all the ground points, this is a must do when tracking down electrical issues.
11-23-2005, 01:32 PM
#5
Burning Brakes
Join Date: Jun 2005
Location: Spokane, WA in the USA
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Indycam,
I've had my C4 only since July. Pump usually runs 15-20 seconds first start of the morning. instant pressue if I go out at lunch. If the car sits all day at work, it'll run for about 10 seconds. Stop & go driving, never even a second. I typically drive the car daily. Last week while out of town for the week, car sat 7 days, pump ran exactly 22 seconds.
I'm not typically a precise person so this added drama of Porsche ownership is trying on my easy going nature.
I know this as I've been timing the pump regulary since finding this board.
I've had my C4 only since July. Pump usually runs 15-20 seconds first start of the morning. instant pressue if I go out at lunch. If the car sits all day at work, it'll run for about 10 seconds. Stop & go driving, never even a second. I typically drive the car daily. Last week while out of town for the week, car sat 7 days, pump ran exactly 22 seconds.
I'm not typically a precise person so this added drama of Porsche ownership is trying on my easy going nature.
I know this as I've been timing the pump regulary since finding this board.
11-23-2005, 02:04 PM
#7
Burning Brakes
Join Date: Jun 2005
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Sure
Send the protocol on over. I'll give it a shot. This could be good timing as I was thinking of bleeding the brakes. I'd be curious to have a baseline to compare with a fresh fluid change. 
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11-23-2005, 02:08 PM
#8
Racer
Thread Starter
Originally Posted by garrett376
Hey Peter - have you removed all of your ground points in the front trunk, cleaned them (wire brush or similar) then reinstalled them? The ground points are usually something like a 10mm bolt to the body sheet metal with wires going to them. I think there are 3 or so of them in the front trunk in various locations.
If the motor is running correctly, but intermittently blows a fuse, then a poor ground could be a source of the fuse blowing. If you have not yet checked all the ground points, this is a must do when tracking down electrical issues.
If the motor is running correctly, but intermittently blows a fuse, then a poor ground could be a source of the fuse blowing. If you have not yet checked all the ground points, this is a must do when tracking down electrical issues.
Thanks!
09-21-2008, 10:09 AM
#10
Racer
Join Date: Feb 2004
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I have a similar problem, no fuse issue but it takes about 30 seconds in the morning to build up pressure before the lights go out. Sometimes the warning beeps two or three times and then turns off. No issues otherwise. It just takes more time than it should to build up pressure. Any thoughts on this one?
09-21-2008, 11:00 AM
#11
Professor of Pending Projects
Rennlist Member
Rennlist Member
Had this happen to me a long time ago... but mine simply stopped working. In your case of blown fuses I would try the suggestion of getting all the contacts clean (negative and the plugs). Any dirt or buildup in the contacts will trigger a blown fuse.
Had a similar situation June 8, 2000.
I was using the car and had to make a sudden stop
at a speed bump. The ABS came to play. Since it was the first time I had sense the system in action I decided to give it another try. It worked flawlessly. Close to my house I made a normal stop and to my surprise the brake pedal would not respond. I had to push it extremly hard to make the car stop.
Here you go:
The problem was solved by: Pressure Sensor replaced(US$247.55 - Part # 964-606-904-00), Relay replaced (US$33.81 Part # 964-615-135-00), Rubber O-Ring replaced(US$4.99 Part # 999-707-094-40). Labor US$147.90 Minus PCA discount.
Try Sunset Imports/Porsche for the parts (did not know about them at the time)... they should have a good price. - http://www.sunsetporsche.com/
A few threads on this:
Best source for PDAS pump and/or pressure switch?
This one gives some more details on the parts:
Stiff brake pedal - No braking!
Let us know how things go... as for a process to test the switch before replacing I don't have one. That procedure would be a great addition to the diy forum here...
Had a similar situation June 8, 2000.
I was using the car and had to make a sudden stop
at a speed bump. The ABS came to play. Since it was the first time I had sense the system in action I decided to give it another try. It worked flawlessly. Close to my house I made a normal stop and to my surprise the brake pedal would not respond. I had to push it extremly hard to make the car stop.
Here you go:
The problem was solved by: Pressure Sensor replaced(US$247.55 - Part # 964-606-904-00), Relay replaced (US$33.81 Part # 964-615-135-00), Rubber O-Ring replaced(US$4.99 Part # 999-707-094-40). Labor US$147.90 Minus PCA discount.
Try Sunset Imports/Porsche for the parts (did not know about them at the time)... they should have a good price. - http://www.sunsetporsche.com/
A few threads on this:
Best source for PDAS pump and/or pressure switch?
This one gives some more details on the parts:
Stiff brake pedal - No braking!
Let us know how things go... as for a process to test the switch before replacing I don't have one. That procedure would be a great addition to the diy forum here...
