PSD Control Off
12-30-2001, 05:11 PM
#1
5th Gear
Thread Starter
Join Date: Dec 2001
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
PSD Control Off
Hi - I'm new to the list so apologies if I'm covering old ground. My name's Dave and I've owned a '90 S4 for over 4 years now - I live in the UK.
Trouble with the PSD system:
The digital dash tells me the PSD Control is off and sure enough the system isn't working. The green PSD indicator dash light does illuminate in wheelspin situations so the sensor side appears to be OK.
Did a brief check down at my local Porsche specialist but was unable to diagnose the problem. Tried to bleed the system using a Bosch Hammer but the hydraulic pump wouldn't stop running - as if it couldn't pressurise the system - I've heard the pressure switches can fail?
The resevoir has lost some fluid but there are no obvious leaks - could it leak from the slave cylinder into the diff? I've disconnected the pump just in case.
Has anyone else experienced similar problems or know a cure?
Any advice would be much appreciated,
Dave
Trouble with the PSD system:
The digital dash tells me the PSD Control is off and sure enough the system isn't working. The green PSD indicator dash light does illuminate in wheelspin situations so the sensor side appears to be OK.
Did a brief check down at my local Porsche specialist but was unable to diagnose the problem. Tried to bleed the system using a Bosch Hammer but the hydraulic pump wouldn't stop running - as if it couldn't pressurise the system - I've heard the pressure switches can fail?
The resevoir has lost some fluid but there are no obvious leaks - could it leak from the slave cylinder into the diff? I've disconnected the pump just in case.
Has anyone else experienced similar problems or know a cure?
Any advice would be much appreciated,
Dave
12-30-2001, 08:57 PM
#2
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Dave,
Sorry to hear your having a problem with the PSD. The reason I'm sorry is due to the fact that almost no one (except maybe the factory and three dealerships)works on these systems. The system does store fault codes that can be read. There is a complete PSD diagnosis section in the workshop manuals (D39-201 to 260). Lots of stuff. Might want to see if a dealer near by has worked on one in the past.
Now for my guess (only a guess). It sounds like the pump is bad. Not producing enough pressure to shut down via the pressure switch.
Normal operation:
The pump fills up the pressure reservior to about 150 BAR and then shuts off via a pressure switch. When the PSD is needed a solenoid opens to apply pressure to the slave cylinder.
Sorry to hear your having a problem with the PSD. The reason I'm sorry is due to the fact that almost no one (except maybe the factory and three dealerships)works on these systems. The system does store fault codes that can be read. There is a complete PSD diagnosis section in the workshop manuals (D39-201 to 260). Lots of stuff. Might want to see if a dealer near by has worked on one in the past.
Now for my guess (only a guess). It sounds like the pump is bad. Not producing enough pressure to shut down via the pressure switch.
Normal operation:
The pump fills up the pressure reservior to about 150 BAR and then shuts off via a pressure switch. When the PSD is needed a solenoid opens to apply pressure to the slave cylinder.
01-03-2002, 01:45 PM
#4
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Join Date: May 2001
Location: Hotlanta - NE of the Perimeter
Posts: 12,269
Received 266 Likes
on
153 Posts
Originally posted by DaveP UK:
<STRONG>Hi - I'm new to the list so apologies if I'm covering old ground. My name's Dave and I've owned a '90 S4 for over 4 years now <snip>
</STRONG>
<STRONG>Hi - I'm new to the list so apologies if I'm covering old ground. My name's Dave and I've owned a '90 S4 for over 4 years now <snip>
</STRONG>
(Sorry - I just noticed the way this thread started - couldn't resist my self
01-05-2002, 04:02 AM
#5
Dave,
I have a 1990 928 S4 and I have recently completed my own servicing of the unit (without the use of a BOSCH Hammer).
Initially your problem sound as though your pressure switch has failed or the pump cannot pump up to the required pressure to activate the switch? (the system operates between 140 & 180 bar) The drawing I have of the running gear shopws that the pressure pump is fitted with the pressure switch, so the problem could possibly located in this combined unit.
Please take care if you bridge out the PSD relay as it appears that if the this relay, located in the spare wheel well, is bridged out whilst pumping up and bleeding the system it may inactivate the pressure cut out switch and could cause over pressure within the accumulator. I have not proved this, but when I bridged out the relay the pump seemed to run too long, however when I used the relay in the circuit and turned the igniton switch to position 2, the pump would cut out on high pressure in a short running time.
If the fault appears to be in the pump or pressure switch it would be advisable to have the system diagnostic tested. I don't think that this is a job that could be a DIY?
To further complicate the issue the PSD is connected to the ABS/lock control unit. The lock control unit is provided on an additional platinum board in the ABS control unit. This unit receives information from the ABS wheel speed sensors, the transverse acceleration sensor, operation of the brakes by the stop light switch, the ABS regulation and the transverse vehicle acceleration (quite complicated). With all these interconnected circuits I would suggest that the fault finding requires a Porsche Centre using a Flashing Code Tester 9268 or Porsche System Tester 9288 as the PSD System is diagnosable and the fault memory can be read by these two diagonostic testers.
You asked whether the brake fluid from the High Pressure Slave Cylinder can leak into the differential.
Whilst writing this reply I'm looking at an end elevation drawing of the Limited Slip Differential and more specifically the slave cylinder. The drawing shows the piston of the slave cylinder has two seal rings and the piston pushes on an actuating rod. The rod appears to go through a seal on the inside end of the slave cylinder and appears to be located inside a consatina seal which butts up against a cap that fits into a recess in the PSD 'Engaging Arm'. This arm give the locking up of the diff via the regulable plate clutch.
The drawing shows that there is a drain hole bored through the slave cylinder after the piston which drains to the outside of the slave cylinder, not into the diff. If you had leaking piston seals you would notice a fluid leak from just outside of the slave cylinder flange where it joins the diff housing.
I would therefore suggest that there should be no contimation of the diff lub oil by the brake fluid from a leaky slave cylinder piston.
I hope that this will assist you.
Tails 1990 928 S4
I have a 1990 928 S4 and I have recently completed my own servicing of the unit (without the use of a BOSCH Hammer).
Initially your problem sound as though your pressure switch has failed or the pump cannot pump up to the required pressure to activate the switch? (the system operates between 140 & 180 bar) The drawing I have of the running gear shopws that the pressure pump is fitted with the pressure switch, so the problem could possibly located in this combined unit.
Please take care if you bridge out the PSD relay as it appears that if the this relay, located in the spare wheel well, is bridged out whilst pumping up and bleeding the system it may inactivate the pressure cut out switch and could cause over pressure within the accumulator. I have not proved this, but when I bridged out the relay the pump seemed to run too long, however when I used the relay in the circuit and turned the igniton switch to position 2, the pump would cut out on high pressure in a short running time.
If the fault appears to be in the pump or pressure switch it would be advisable to have the system diagnostic tested. I don't think that this is a job that could be a DIY?
To further complicate the issue the PSD is connected to the ABS/lock control unit. The lock control unit is provided on an additional platinum board in the ABS control unit. This unit receives information from the ABS wheel speed sensors, the transverse acceleration sensor, operation of the brakes by the stop light switch, the ABS regulation and the transverse vehicle acceleration (quite complicated). With all these interconnected circuits I would suggest that the fault finding requires a Porsche Centre using a Flashing Code Tester 9268 or Porsche System Tester 9288 as the PSD System is diagnosable and the fault memory can be read by these two diagonostic testers.
You asked whether the brake fluid from the High Pressure Slave Cylinder can leak into the differential.
Whilst writing this reply I'm looking at an end elevation drawing of the Limited Slip Differential and more specifically the slave cylinder. The drawing shows the piston of the slave cylinder has two seal rings and the piston pushes on an actuating rod. The rod appears to go through a seal on the inside end of the slave cylinder and appears to be located inside a consatina seal which butts up against a cap that fits into a recess in the PSD 'Engaging Arm'. This arm give the locking up of the diff via the regulable plate clutch.
The drawing shows that there is a drain hole bored through the slave cylinder after the piston which drains to the outside of the slave cylinder, not into the diff. If you had leaking piston seals you would notice a fluid leak from just outside of the slave cylinder flange where it joins the diff housing.
I would therefore suggest that there should be no contimation of the diff lub oil by the brake fluid from a leaky slave cylinder piston.
I hope that this will assist you.
Tails 1990 928 S4
01-09-2002, 03:46 PM
#6
5th Gear
Thread Starter
Join Date: Dec 2001
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for all the replies - still working the problem out but I now have the relevant pages from the Workshop Manual. If I find an obvious solution, I'll let you all know.
Dave
Less
Dave
Less
