Another PSD question!
01-13-2005, 04:50 PM
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Another PSD question!
My 1990 that I just purchased had 3 indicators on the dash Toothed Belt (fixed). The next one I'm going after is Differential Control Off (PSD). According to what I've read. The fact that the ABS light is not on indicates that the problem is most likely with the hydraulic system in the wheel well. I've read and printed the proceedure and intend on doing a system flush and refill this weekend. My question is........ I've seen at least 2 post where the pump was thought to be air bound. The pump appeared okay but would simply NOT pump. Does anyone know if and how this issue was resolved? The post stop shy on the fix! 
01-13-2005, 06:06 PM
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In one case I'm aware in Finland debugging is still ongoing. Next plan is to create pressure on both sides of pump to help it to start making more on it's own. Or so theory goes, remains to be seen if it works in practise. Seems pump itself is healthy but just can't make enough initial pressure to get process going again. Is there pressure in container when it is delivered as spare part? On my pumps container there still is after almost two years of inactivity. This leads me to believe there's supposed to be significant one permanently and pump might not be able to restore it if it's lost for some reason.
01-13-2005, 09:32 PM
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There is an excellent paper on PSD service on the 928 Owners Club website (www.928oc.org), click on Services and select Journal. The article is "PSD System Bleeding, A speedy alternative to the factory procedure"
If you haven't serviced your PSD unit, the odds are it is in need of service (flushing). Do it before it gets clogged up. Most shops do not know about servicing the PSD and you don't find out until the light comes on and it is too late!
If you haven't serviced your PSD unit, the odds are it is in need of service (flushing). Do it before it gets clogged up. Most shops do not know about servicing the PSD and you don't find out until the light comes on and it is too late!
01-13-2005, 11:55 PM
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What's the third indicator light? You should fix the PSD problem before performing any PSD maintenance, otherwise you might be doing it twice.
If you let the pump run dry, after refilling the reservoir, it's difficult to remove trapped air in the pump impeller. The WSM also states this.
I recently drove my S4 with the PSD pump solenoid valve electrically disconnected and got that same warning as soon as the wheels moved. So I know, in addition to the pump not building up pressure, the warning can come from the controller not sensing the solenoid valve.
Another time, I had my S4 smogged on a machine that allows the rear wheels to spin on rollers while the front wheels were stationary. The same warning came on while the car was tested. So you might have a wheel sensor problem.
If you let the pump run dry, after refilling the reservoir, it's difficult to remove trapped air in the pump impeller. The WSM also states this.
I recently drove my S4 with the PSD pump solenoid valve electrically disconnected and got that same warning as soon as the wheels moved. So I know, in addition to the pump not building up pressure, the warning can come from the controller not sensing the solenoid valve.
Another time, I had my S4 smogged on a machine that allows the rear wheels to spin on rollers while the front wheels were stationary. The same warning came on while the car was tested. So you might have a wheel sensor problem.
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01-14-2005, 10:57 AM
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There is a pump relay in the spare tire wheel well. I suggest you get a copy of the workshop manual so you have a better understanding of the complete system.
Might be time saving and $$ saving to get someone with the Bosch Hammer to pull the error codes for the PSD. Porsche dealer should have one or a really good Porsche shop.
Might be time saving and $$ saving to get someone with the Bosch Hammer to pull the error codes for the PSD. Porsche dealer should have one or a really good Porsche shop.
01-14-2005, 11:24 AM
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I have a copy of manuals, that's where I read the comment about if the ABS light isn't on look at the hydraulics system. I did go to the fuse next to the relay in the spare tire compartment and found it to be good. I'll check the power and relay and get into the pump section this weekend. I'm just trying to gather as much info. as possible before hand. Im looking forward to trouble shooting the issue and hope to have good news come Monday..............."Come Monday it'll be alright................."
01-14-2005, 03:38 PM
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Went home at lunch today, took off the cover that hides the PSD pump (wheel still on), resivoir dry, checked voltage to the pump (12V), checked motor resistance (open) BAD MOTOR!, connected power to the motor, taped on the motor with a wrench (it ran). NOW............. I guess at this point I need to take the motor out, clean it (probably dirty/rusty), refill the system, look for leaks and bleed it............... HOPEFULLY!
