PDAS/ABS and warning light problem (long post)
11-03-2005, 06:21 AM
#1
AutoX
Thread Starter
Join Date: Oct 2005
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
PDAS/ABS and warning light problem (long post)
As a newbie to the 964 I read quite thoroughly the parts of Adrian’s book that cover the ABS and PDAS systems. I also went through the technical articles on the Rennlist and read quite a few older threads on the subject. However, I didn't come across an identical match with my problems and as I'm technically not very savvy, I'm a bit lost...
By the way, I have a ’92 964 Carrera 4.
The “problems” I have relate to brake pressure and the warning lights. The problems might be related or not, I am not quite sure…
First of all I was due to have a brake fluid change as it was two years since the last change. My OPC assessed that I had a problem with brake pressure and that the brake pressure reservoir was leaking. The symptom was that the brake pressure pump went on, on the second hit on the brake pedal. OK, so I had the OPC install a new brake pressure reservoir, pressure switch and relay. Also the rear brake pressure valve was changed to a new one as the bolt broke on the old one.
After all these repairs, the “problem” still remained, with the pump going on after the second hit on the brakes and the pedal going “soft” all the way to the floor after that. This is when the OPC did a complete brake pressure test according to factory protocol and found no leaks in the system.
According to my OPC, the maximum pressure in the system is 165bar and minimum 140bar
The lowest figure during testing that was recorded was 141bar, so it’s in factory spec.
During a 30min leak test according to factory standards gave a result of 149bar, the minimum accepted being 140bar.
The pump itself was also tested and should be OK. When I put on the ignition in the morning it only takes about 20 seconds to fill the pressure reservoir. And every time the pump goes on after this, it only works for about 5-6 seconds at a time.
I also have tested the manual traction control and it works as it should, the led blinks and it turns itself off at around 40km/h. Also the PDAS seems to work, at least the small yellow led blinks on slippery roads… and the rear spoiler works OK. So the differential locks should be OK.
Any ideas what could be the cause of this "problem" and is it really a problem?
Someone suggested brake master cylinder, but the OPC assured that all pressure issues have been checked and everything is according to factory standards.
The second problem is a warning light problem. First of all, all my warning lights light up normally when I turn on the ignition, but when I start the car all warning lights go off immediately. As I understood from Adrian’s book the PDAS and ABS lights should stay on until the pump has filled the pressure. Secondly, at some occasions, especially when it’s cold and damp, the PDAS and brake pressure warning lights light up and will not go off until the engine is turned off. In the mean time the pump works just the same way as it does when the warning lights are not on.
One reason for this erratic behavior can be my battery which has seen its best days. Another reason might be the dodgy coil cables that have “hit through”. The cables will be switched to new ones at the OPC next Tuesday and I think I’ll replace the battery with a new one as well.
Sorry for the rather lengthy explanation. I would certainly appreciate it if you could give me any pointers on how to solve these issues. Based on reading Adrian’s book and technical reports I tend to suspect the control unit or the solenoid valves. I don’t know if its relevant here but I have changed my tires from 17” Cup-1’s on summer tires to 16” Cup-1’s on winter tires, however the problems were pretty much the same also with the summer tires...
Thanks a million in advance!
Ilkka
Helsinki, Finland
By the way, I have a ’92 964 Carrera 4.
The “problems” I have relate to brake pressure and the warning lights. The problems might be related or not, I am not quite sure…
First of all I was due to have a brake fluid change as it was two years since the last change. My OPC assessed that I had a problem with brake pressure and that the brake pressure reservoir was leaking. The symptom was that the brake pressure pump went on, on the second hit on the brake pedal. OK, so I had the OPC install a new brake pressure reservoir, pressure switch and relay. Also the rear brake pressure valve was changed to a new one as the bolt broke on the old one.
After all these repairs, the “problem” still remained, with the pump going on after the second hit on the brakes and the pedal going “soft” all the way to the floor after that. This is when the OPC did a complete brake pressure test according to factory protocol and found no leaks in the system.
According to my OPC, the maximum pressure in the system is 165bar and minimum 140bar
The lowest figure during testing that was recorded was 141bar, so it’s in factory spec.
During a 30min leak test according to factory standards gave a result of 149bar, the minimum accepted being 140bar.
The pump itself was also tested and should be OK. When I put on the ignition in the morning it only takes about 20 seconds to fill the pressure reservoir. And every time the pump goes on after this, it only works for about 5-6 seconds at a time.
I also have tested the manual traction control and it works as it should, the led blinks and it turns itself off at around 40km/h. Also the PDAS seems to work, at least the small yellow led blinks on slippery roads… and the rear spoiler works OK. So the differential locks should be OK.
Any ideas what could be the cause of this "problem" and is it really a problem?
Someone suggested brake master cylinder, but the OPC assured that all pressure issues have been checked and everything is according to factory standards.
The second problem is a warning light problem. First of all, all my warning lights light up normally when I turn on the ignition, but when I start the car all warning lights go off immediately. As I understood from Adrian’s book the PDAS and ABS lights should stay on until the pump has filled the pressure. Secondly, at some occasions, especially when it’s cold and damp, the PDAS and brake pressure warning lights light up and will not go off until the engine is turned off. In the mean time the pump works just the same way as it does when the warning lights are not on.
One reason for this erratic behavior can be my battery which has seen its best days. Another reason might be the dodgy coil cables that have “hit through”. The cables will be switched to new ones at the OPC next Tuesday and I think I’ll replace the battery with a new one as well.
Sorry for the rather lengthy explanation. I would certainly appreciate it if you could give me any pointers on how to solve these issues. Based on reading Adrian’s book and technical reports I tend to suspect the control unit or the solenoid valves. I don’t know if its relevant here but I have changed my tires from 17” Cup-1’s on summer tires to 16” Cup-1’s on winter tires, however the problems were pretty much the same also with the summer tires...
Thanks a million in advance!
Ilkka
Helsinki, Finland
11-03-2005, 08:21 AM
#2
First of all, all my warning lights light up normally when I turn on the ignition, but when I start the car all warning lights go off immediately. As I understood from Adrian’s book the PDAS and ABS lights should stay on until the pump has filled the pressure. Secondly, at some occasions, especially when it’s cold and damp, the PDAS and brake pressure warning lights light up and will not go off until the engine is turned off. In the mean time the pump works just the same way as it does when the warning lights are not on.
However - about the warning lights :
It depends. If the accumulator is fully charged then the pump has no reason to run and the lights will go off straight away. I usually find that the first time I use the car in the morning, the lights will stay on for 15s or so, but for the rest of the day they will go out straight away. A few years ago, I replaced the hydraulic unit and for a while after that, my pump didn't even activate first thing in the morning. These days I only use the car at weekends and sometimes they stay on long enough for the buzzer to activate (but only for a few seconds).
For the warning lights coming on / staying on - they are quite sensitive to battery voltage so a poor battery may not be helping although if you're not at idle I would expect the alternator to be making up for it. However - when I first got my car I had the problem that these two lights would come on at startup and would not go off until I hit over 3000rpm. This was actually the clock (the one that tells the time). Replaced the clock and the problem went away. I'm not sure how you can check this without trying a new one - but it might be worth replacing the battery, checking the alternator output - and ideally borrowing a clock if you can find one close by.
11-03-2005, 04:08 PM
#3
Advanced
Join Date: Oct 2005
Location: Australia
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
Sea Eagle
I had a similar issue witht he PDAs light and the buzzer. It was Worse when the car had not ben driven for a while.
Spoke to my reliable porsche expert mechanic, who said if they go off relatively soon, nothing to worry about. They always went of and the buzzer stopped after 7 seconds at most. Took it in for its 20,000km major servce, where everything was bled, adjusted, oil replaced etc. etc and there are no more examples of this issue. Not even after a small peirod of non use.
My view, if the lights go out, and the buzzer goes off, and the hydraulics etc aren't leaking and have been bled, nothing to worry about (assuming your brakes and clutch etc work fine). Not sure about your mechanic but you need someone who is truly proficient with these vehicles if you are not yourself.
Spoke to my reliable porsche expert mechanic, who said if they go off relatively soon, nothing to worry about. They always went of and the buzzer stopped after 7 seconds at most. Took it in for its 20,000km major servce, where everything was bled, adjusted, oil replaced etc. etc and there are no more examples of this issue. Not even after a small peirod of non use.
My view, if the lights go out, and the buzzer goes off, and the hydraulics etc aren't leaking and have been bled, nothing to worry about (assuming your brakes and clutch etc work fine). Not sure about your mechanic but you need someone who is truly proficient with these vehicles if you are not yourself.
11-03-2005, 04:32 PM
#4
RL Community Team
Rennlist Member
Rennlist Member
Originally Posted by 964fin
First of all I was due to have a brake fluid change as it was two years since the last change. My OPC assessed that I had a problem with brake pressure and that the brake pressure reservoir was leaking. The symptom was that the brake pressure pump went on, on the second hit on the brake pedal.
After all these repairs, the “problem” still remained, with the pump going on after the second hit on the brakes and the pedal going “soft” all the way to the floor after that. This is when the OPC did a complete brake pressure test according to factory protocol and found no leaks in the system.
Any ideas what could be the cause of this "problem" and is it really a problem?
Sounds like this may be the first C4 your mechanic has ever seen! Especially if everything checks out... where is the problem?!
The second problem is a warning light problem. First of all, all my warning lights light up normally when I turn on the ignition, but when I start the car all warning lights go off immediately. As I understood from Adrian’s book the PDAS and ABS lights should stay on until the pump has filled the pressure.
Secondly, at some occasions, especially when it’s cold and damp, the PDAS and brake pressure warning lights light up and will not go off until the engine is turned off. In the mean time the pump works just the same way as it does when the warning lights are not on.
Check your brake fluid level sender! Low fluid will activate these warnings and other systems will function just fine.
Good luck!
11-03-2005, 05:30 PM
#5
Super Duper Moderator
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Originally Posted by 964fin
First of all, all my warning lights light up normally when I turn on the ignition, but when I start the car all warning lights go off immediately. As I understood from Adrian’s book the PDAS and ABS lights should stay on until the pump has filled the pressure.
This does not sound like a problem as Garrett has said also.
Marc
11-04-2005, 05:44 PM
#6
AutoX
Thread Starter
Join Date: Oct 2005
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
Thanks guys for the replys!
As you might guess, there is not very much knowledge over here on the specific issues of the 964. There is only one OPC here in Finland that was established in '98 so they don't have extensive experience on 964's and they actually bought the 964 diagnostic tools from the factory because they could't figure out "manully" if there was a problem with my brakes or nor...
In normal conditions the warning lights don't light up when the pump goes on, so I suspect the pressure in the system is at an OK level as indicated by the OPC measurements.
To further explore the warning light "problem" I'll have to change the battery and the coil leads first, as they need to be replaced anyway, and see if that has any effect on the "problems". I like to think the warning lights lighting up and not going out until the engine is turned off is an electrical problem caused by a weak battery or bad coil leads. I never get the buzzer sound when the lights go on for a long time. The only exception is when I really step on the brakes for a dozen or so times at idle. Then the lights go on and the buzzer goes on as I gues they should.
Garrett, I hope we're chasing a problem thats not an actual problem At this point I'll have to give a big hand for the OPC for not charging me anything for their "practice" sessions with the diagnostic tools and the unnessessarily changed items... They are about as eager to know whats happening as I am. Its just that brakes are a rather important part of a car and I'd rather be really sure that everythings OK. I would not want to experience total brake failure like some Rennlisters have...
Garrett, the first problem is that although the pressure checks out, the pedal still goes soft after the second hit on the brakes and I don't think this is how things should work. (No warning lights here)
Regarding the second problem I have understood that when you cold start the engine the PDAS/ABS warning lights should be on until the pump has pressurised the system. My lights go off immediately but the pump still continues to fill the pressure.
I'll have to check the brake fluid level sender as well.
I'll be back at the OPC next Tuesday for my weekly appointment I hope this is not going to become a habit...
As you might guess, there is not very much knowledge over here on the specific issues of the 964. There is only one OPC here in Finland that was established in '98 so they don't have extensive experience on 964's and they actually bought the 964 diagnostic tools from the factory because they could't figure out "manully" if there was a problem with my brakes or nor...
In normal conditions the warning lights don't light up when the pump goes on, so I suspect the pressure in the system is at an OK level as indicated by the OPC measurements.
To further explore the warning light "problem" I'll have to change the battery and the coil leads first, as they need to be replaced anyway, and see if that has any effect on the "problems". I like to think the warning lights lighting up and not going out until the engine is turned off is an electrical problem caused by a weak battery or bad coil leads. I never get the buzzer sound when the lights go on for a long time. The only exception is when I really step on the brakes for a dozen or so times at idle. Then the lights go on and the buzzer goes on as I gues they should.
Garrett, I hope we're chasing a problem thats not an actual problem
At this point I'll have to give a big hand for the OPC for not charging me anything for their "practice" sessions with the diagnostic tools and the unnessessarily changed items... They are about as eager to know whats happening as I am. Its just that brakes are a rather important part of a car and I'd rather be really sure that everythings OK. I would not want to experience total brake failure like some Rennlisters have...Garrett, the first problem is that although the pressure checks out, the pedal still goes soft after the second hit on the brakes and I don't think this is how things should work. (No warning lights here)
Regarding the second problem I have understood that when you cold start the engine the PDAS/ABS warning lights should be on until the pump has pressurised the system. My lights go off immediately but the pump still continues to fill the pressure.
I'll have to check the brake fluid level sender as well.
I'll be back at the OPC next Tuesday for my weekly appointment
I hope this is not going to become a habit...
11-04-2005, 06:38 PM
#7
RL Community Team
Rennlist Member
Rennlist Member
Originally Posted by 964fin
I never get the buzzer sound when the lights go on for a long time. The only exception is when I really step on the brakes for a dozen or so times at idle. Then the lights go on and the buzzer goes on as I gues they should.
Garrett, the first problem is that although the pressure checks out, the pedal still goes soft after the second hit on the brakes and I don't think this is how things should work. (No warning lights here)
If you don't like the feel of the pedal, you may need to look at your flexible brake lines - as you may have old rubber ones needing replacement. That has been said to cause a softer pedal (I've never noticed this issue, but I've heard people mention it).
My lights go off immediately but the pump still continues to fill the pressure.
I'll have to check the brake fluid level sender as well.
Trending Topics
11-08-2005, 11:17 AM
#8
AutoX
Thread Starter
Join Date: Oct 2005
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
New coil leads and a new battery have seemed to help with the erratic behaviour of the warning lights. My OPC also run a check of all fault codes without anything out of ordinary, so I guess my brakes are OK. The only thing that still slightly bothers me, is that on the second hit on the brake pedal the pedal goes all the way to the floor. However, the brakes still work OK and the car stops as it should. It might be good idea to check the condition of the brake lines anyway
