PSD pump that became standard feature in the 1990 Porsche 928 S4/GT and later in the GTS

Did you know that there's a filter in the PSD reservoir?

It is not serviceable, but the reservoir is about 30 euro's. **note in 2013: it is impossible to purchase as stock was used up worldwide.

One option is to remove the filter inside the reservoir and add an external one like in this picture.

The relay could touch ground. Here's some extra foam isolation applied to prevent this.

PSD pump fuse next to the relay

The PSD will start to lock the rear wheels under hard straight line acceleration if a speed difference of 2 km/h or more is present between rear wheels. As soon as a speed of 30 km/h is reached the PSD will stop the action again.

If you go faster than 60 km/h and you are in a turn and the system notices deceleration, the system is activated to prevent oversteer.