martinss

I am getting the PSD inactivation warning on my '90 S4 Euro.

A little history. I've had the car since August. When I got it the error would come up after driving for a few minutes.

When I looked at the unit for the first time, I found the reservoir very low. I refilled and hoped that would solve the issue. For a while I did not get the error, then after a few days it reoccurred.

I then ran through a full PSD flush (Louis Ott and John Veninger method). There was foam/bubbles in the system (consistent with it running low), and the brake fluid was a light amber (i.e. not really dark, but not fresh either). I did an extensive flush (used over 2 pints) until the fluid was completely clear.

However, when I went back on the road the error occurred again in as short a time traveled.

I realize I can get a diagnostic tool and check for electrical error codes. I am looking into find one local to me (Toronto area). Failing that I could request the one from the 928 OC tool loan program.

I also understand that a hydraulic issue cannot be diagnosed by the tool.

Here are some observations from my flush that may eliminate some possibilities:

1. During the flush, after closing a bleed screw, the pump would run for about 5-8 seconds, with steadily rising note and then shut off. It seems therefore that it is able to generate the required pressure and that the pressure could be held for a few minutes at least
2. When flushing the lock control valve at the differential, I got a good flow of fluid with the bleed screw open, so it seems that the valve is able to open and close (but I suspect not fully closing as noted below)
3. The relay click could be heard when jumping that valve

Last night I moved the car in my driveway after a rain storm. I realized that the PSD was active as the rear tires were scrabbling on a sharp, low speed turn. My assumption is that the differential should be fully open under this condition, which suggests to me at least that there is a bleed through of pressure that is partially locking the differential. So the lock control valve is suspect in my mind.

Thoughts please?

Herman K

Do you have a copy of the factory PSD service manual?

If not send me a PM with yr e-mail and I get you a copy!

NoVector

Hi Herman - Can you please send me a copy too? I just bought a spare and plan on going through it this winter. Thanks!

928 at last

Martin,
I've got Theo's diagnostic software.
Could be your lateral acceleration sensor needs some TLC. That was my issue when the PSD was going off.

TheoJ

hi, an error check would certainly help. No, the system does not report hydraulic pressure, but I assume you have pressure as flushing works, and the pump stops after 5 seconds. So it is important to find out now what therror means.
regards
Theo, 1992 GTS

martinss

Thanks Rob - will PM you.

Thanks Theo - that is my aim.

martinss

I visited Bob (928 at last) this morning and he was kind enough to run the diagnostics with Theo's software. Two errors showed - one for the yaw sensor and one for the transverse lock. Bob had the same errors with his '90 and resolved them by cleaning the sensor.

So I took mine apart. The copper-coloured swinging pendulum was seized so that it could not easily move from side to side - it stayed wherever I pushed it. I sprayed copious amounts of contact cleaner in, but this only partially cleared the pendulum. I found that the core of the magnet above which it floats was corroded - flakes and filings remain stuck to it since it is magnetic. I had to use a sliver of business card to slide under the pendulum to work the debris out, then scrape it off with a screwdriver. Once I had finished the pendulum moved freely.

Placing the sensor on either side (1g lateral) showed that the pendulum would move to that side, but not completely. Shaking the sensor in either direction (>1g) produced a click as the pendulum touched the side - btw, this would be a quick diagnostic test without even having to open the sensor.

Here is a pic of the cleaning process showing some of the debris removed and the card inserted:



So the sensor was certainly defective, and I think I have cleaned it sufficiently to restore normal function. Hopefully the transverse lock error does not indicate an independent issue. Tomorrow I'll get a chance to give it a good drive to find out...

martinss

Well I took the car for a 50km run, with several stops. And I exercised the PSD function. No errors. Yeah!

Tom in Austin

Very interesting, I've seen commentary that the 928 lat sensor was an old or poor design, this helps explain better. I'm going to open mine up too, my car gave the mysterious "implausible value" error and I believe the manual says this can be from the lat sensor, so definitely worth trying.

Rob Edwards

Just for cross-referencing, some additional threads on the accelerometer.

https://rennlist.com/forums/928-foru...t-working.html



And John Speake makes a replacement if anyone's sensor is well and truly FUBAR. Post #12:

https://rennlist.com/forums/928-foru...on-sensor.html

928 at last

AO

Got to remember this one! I presume this is located under the driver's seat?

martinss

Yep. See pic of rear edge of seat - is small box with green label held in by two Phillips screws on the right:

martinss

I wish he posted the price on his website. Personally when I see something like, "For availability and pricing, Email JDSPorsche," I look for an alternative. I want list price posted and a sense that everyone pays a similar price.

AO

Thanks Martin. I will add it to the list of things to inspect when the GT goes down for it's winter nap.