PDAS light help needed please

[NZ C4]

Hi Everyone, recently purchased my first Porsche (1990 C4 manual) and loving the experience so far but trying to work through a few issues it currently has.
When I got it the ABS and Traction lights had been removed (obviously they were on all the time) so have been chipping away at diagnosing these.

After doing a bunch of maintenance work and diagnosing the ABS works now (jumper in the relay) but I'm left with the following:
Start car and all lights go out within 10 sec, start driving all is fine and ABS is working when braking hard, drive about 1km the PDAS light comes on along with the alarm, keep driving and ABS is still working but a little later (5min) the ABS light comes on as well followed by the hyd pressure light a few minutes after that.

Done to date are full fluid flush, calipers, clutch, accumulator, dual solenoid and managed to bleed the rear PDAS lock (have not yet removed the belly pan to bleed the front one)
Fluid in the system was pretty clean to begin with so someone has done it before.

Cleaned all ABS sensors and checked grounds, all sensors range 1000ohm to 1015 ohm so seem ok. (speedo is working also, as is the clock)

Removed and cleaned both accelerometers and cleaned them, seemed pretty clean already.

Checked and cleaned all grounds for ABS pump, brake fluid is just over max with system pressurised, contacts in the cap are working.

When the engine has been running and system is pressurised it takes about 30 pumps of the pedal for the pedal to go rock hard.
How does one test if the accumulator is ok?
Have done a lot of searching but have not found anything with the exact symptoms mine has?

[Hamptonsam]

Is the abs brain mounted with the 55 pin connector on top? If so, there could be corrosions on the pins. If you have not removed the plug, be very careful. I had so much corrosion that a pin broke off. The unit is NLA and used ones cost a fortune.

[porterdog]

Is your fluid level at Max with the engine running? Quite a few guys have gotten hung up by that.

[umgang]

Originally Posted by porterdog

Is your fluid level at Max with the engine running? Quite a few guys have gotten hung up by that.

the 964 sensor on brake fluid reservoir is sensitive but usually intermittent if slightly low.
Hydraulic pump could be acting up in front boot.
Also check your lateral and longitudinal actuation cylinders-
are you losing brake fluid ?

[NZ C4]

Thanks for the replies, yes the brake fluid is just over max with engine running.

Checked connector on ABS brain, looks like new and no pins damaged or corroded

Not loosing fluid that I can see, should I remove the actuator cylinders to inspect them?
Sensor on the reservoir is working, checked with circuit tester.

[umgang]

if not losing fluid than slaves are probably ok

[NZ C4]

Anyone know how the ABS ecu realizes faults in the PDAS sytem?
Thing that has me stumped is that everything seems ok until having
driven a short distance.

[porterdog]

Does your pressure pump run for too long? If the system takes too long to get to the cutoff pressure the alarm will sound.

[techman1]

Does the cutoff happen after time only, or distance?

[NZ C4]

Looked at this again after it sat over the weekend and noticed that the brake fluid level had dropped from where I left it on Friday (have only just got this car) so I dropped all of the belly pans and found the longitudenal lock to be leaking.
Will remove both of them and open them up, by the amount of postings on the locks I'd be surprised if that doesn't fix it.

Tested most other parts now which seem to be fine however have not found a way to test the bomb yet.

[porterdog]

Originally Posted by techman1

Does the cutoff happen after time only, or distance?

Cutoff occurs when the pressure switch closes (?) indicating target pressure has been reached. The alarm is based on time, I believe.

[porterdog]

Originally Posted by NZ C4

Looked at this again after it sat over the weekend and noticed that the brake fluid level had dropped from where I left it on Friday (have only just got this car) so I dropped all of the belly pans and found the longitudenal lock to be leaking.
Will remove both of them and open them up, by the amount of postings on the locks I'd be surprised if that doesn't fix it.

Tested most other parts now which seem to be fine however have not found a way to test the bomb yet.

9meister out of the UK sell a difflock actuator seal kit.

[NZ C4]

Thanks for the tip, will contact them today.

[NZ C4]

Contacted 9meister today and got a response right away from Colin so have ordered a set, for those who may not know the cost was 62 pounds for a set to do 1 car and included postage.

[NZ C4]

New seal kits arrived from 9Meister and fitted, holding fluid level now but still have issues, how does one test the accumulator??
Ign on and system up to pressure I get 2 pumps and on the 3rd the pump starts again for about 4-5 seconds then shuts off.
Also what is this plug for? Am I missing a component?

[perelet]

Here is one thing that I know about hydraulic booster system (cause I'm adopting c4 hydraulic booster to my C2 - RS had similar setup).

1. Light on console is wired directly to pressure switch and pump. There's no electrical connection between ABS unit and booster pump/pressure switch.

If you very bored you can trace electrical diagram for connections.

[NZ C4]

Anyone know what that plug is for? how to test the accumulator...........anybody?

[NZ C4]

Had the car scanned today and had this fault
44 fault cond 18 front rear diff lock deviations code 18
Both lock cylinders have been re kitted, any ideas where to look next?
Can someone also check if the pictured plug goes anywhere on their C4 please?
Not really sure where to look next.

[ffc]

I have the loose plug as well. 1990 C4 Targa (see below). I found a picture on rennlist as well showing the plug not in use as well. PM me for the link if you wish. I am not sure about the etiquette of pointing to other forums on here.

[napaul]

I think that plug goes to the headlight washer pump if it was equipped.