I decided to spring for a used DSC module, The ABS light went off and all seemed good until the DSC light came back on but not the ABS light, progress!

 Here you can see photos of the failed module

note blown capacitor and brunt tracings on circuit board as compared to replacement module..

Below the replacement module

, The ABS light went off and all seemed good until the DSC light came back on but not the ABS light, progress! The fault was the lateral sensor which at first I mistook for the yaw sensor. disconnecting the yaw sensor and reading the faults got me back on track.

Looking up parts on RealOEMBMW the 

https://www.realoem.com/bmw/enUS/showparts?id=CH93-USA-10-1999-Z3-BMW-Z3_25&diagId=34_0917

parts are listed as Speed  Sensor and Acelleration Sensor



The parts in the drawing do not look like the parts in real life

 34526864094 Speed sensor....comes up in INPA yaw sensor in the ETM (Electrical Troubleshooting Manual) it is listed as RPM Rate Sensor

37146781403 Accelerating sensor...Lateral sensor in the ETM Tansverse Accelaration Sensor 

The Lateral sensor replaced went for a test drive and the DSC light came back on again This time it was #177 preload pump electrical failure. I could not active the pump motor with INPA. Looking at the wiring diagram I saw that fuse 51 (30 amp) in the aux fuse box  seemed to be tied to the pump 

I checked it was blown. I replaced the fuse

 

test drive the DSC light came on again note all these times the DSC light comes on when driving slightly over 20mph.

The fault this time is #178 preload pump actuation error.

trying to find out what error # 178 Preload Pump Actuation Error means ? what set this fault?

I have not found very much information on Treves MK20 faults.

I coding the DSC with NCS Expert 

The ABS works and under 20 mph the DSC also works.

What Popped the fuse?  There was no dead short to ground because it did not blow again.  

The fuse did not appeared to have blown by a sudden overload such as a dead short to ground but slow deterioration of the material,l unfortunately the linked photo shows the fuse after the center material fell out when handling it. I am thinking it was a high drawn from the DSC module over a period of time see the photos of the failed module circuit board and capacitors.

I am thinking that Preload Pump Actuation error can only be tripped by by pressure sensors, I bled the brake system. I had bled the system before when the DSC/ABS was off line and was not able to activate the pumps.  

There are two pumps in the system

I was able to activate  but the Precharge but whenactivate there was no flow from the bleeders....

The Treves MK20 DSC was used for only a short time so there was not much information on replacing it.

The prechaege pump is locatedon the left side below the brake master cylinder. some access can be gained by removing the left front tire and then the fender main splash sheild  the is a seconday sheild covering the Precharge pump

There is a web site that shows the mounting of the Precharge on an E39 /E39

http://www.meeknet.co.uk/e38/ABS/Index.htm

The pump needs to be removed from the mount before it can be removed. Disconnecting the two lines from the master cylinder appears to be the way to go as access to the lines is limited. Once the lines disconnected and pump is removed from the mount it can be lifted out. The mount is difficult to disconcern in its location, the photos below and the link above will help in its understanding. The E39 link above shows the pump being removed with the mount , this is not possible on the Z3 

The Pump did not blow the fuse after it was replaced so it could be assumed that it was not shorted to ground. Checking continunity on the motor leads it was found to be ok, that ruled out worn brushes as there would be an open circuit. Worn brushes are often cited in different forums as the cause of Prepump failure. I have found in my experience permanent magnet DC motor to be pretty robust

I disassembed the prepump.

The motor sperated from pump. The pump runs when disassembed some heat discoloration of one of the motor armature windings. The brushes were in good condition.

The motor is drive by a short cable. Who remembers when speedometers were driven by a cable?

there is a spacer between the pump and motor

The pump was siezed 

The pump is a small gear pump

The failure was due to lack of maintenance specifically a proper brake flush.  The brake flush needs to include activation of both pumps in this system.