Help with ABS problem please

[gunman]

Do you mean fuse 31?
I would still try to communicate with the ecu by removing the K lines for the other ecus one at a time or remove the ecu connector and trace back to the K line for the ABS ecu. Whilst you are there you can check for power at the ecu connector. If you have power and earth and the K line is still connected and you still don't get a response then maybe its time to start replacing stuff.
However there is nothing more frustrating than randomly replacing stuff only for the fault to remain!
I might be able to give you some clue about what pins to check at the ecu connector if you are interested in doing it that way. Unfortunately the later ABS does not seem well documented.

Yes, sorry, I meant Fuse 31. Any help on what to test would be well received.

I have an ABS control unit you can have for the cost of postage, to be honest they very rarely go wrong so I never sell them.

A very kind offer, I will PM you, thanks.

[twoqu]

Dowmload this for study. I beleieve this is the same as the S2 one before the S6 got the later Bosch 5 stuff.

http://www.volkspage.net/technik/ssp/ssp/SSP_148.PDF

Scroll down to the wiring schematic and you should be able to work out what gets power and earth and what the k line pin is. You will have to ignore the fuse designations as they are for the C4!
My argument is that the ecu will tell you what is up if you can connect, so its worthwhile eliminating an electrical problem first before condemming components unless of course you have something obviously hanging off or disconnected!

[twoqu]

I think this one is ok but for obvious reasons its better to get one from the exact year! At least it shows the K line!

http://www.s2central.net/S2_Schematics/B/B58.PDF

[gunman]

Thanks

I'll have a look at that, I will admit that wiring diagrams are not my strong point but I'll give it a go and see. May be a few days before I get a chance to check it out again.

[twoqu]

Well pin 1 should have 12V ignition on.
Pin 16 should have 12V battery perm.
Pin 20 & 34 should be earthed.
Pin 31 is the K line back to the fuse box.
So you can at least eliminate those quickly. I would remove each K line and test it back to get the ABS controller one identified and then just connect that one and the 2X2 connector back up if you have all the power and earths. If you cannot connect to it then, it might be faulty although as previously mentioned these are pretty reliable. Due to the differences in the systems be sure to replace like for like by X ref the controller p/n.

[Tommy200rs]

Here some selfhelp for those series 1 ABS unit that does not have support in vagcom diagnostics.
Validity from ETKA for ABS ecus sitting under rear seat.
Most problems are due to ABS sensor faults. Can be resistance problem or distance problem at the sensor
to the drive shatft sender "ring" or metal dust particles at the end of the magnetic sensor
(similar powder can be problem alsofor flywheel sensor)
or that the metal from the ring has rusted away too much

Etka code in abs ecu (used in audi 80q, 100q, 200q etc...) :
ABS unit 2B2
0265103032 (bosch, discontinued)
857 907 379 D (vag)

0265103033 (bosch replacement, discontinued)

8A0927807A sensor rear

https://www.google.fi/search?q=audi+80+abs+sensor&rlz=1C1CHJW_enFI567FI567&es_sm=122&source=lnms&tbm=isch&sa=X&ei=TdOOU5-IMMaN7QaK9YC4Cg&ved=0CAgQ_AUoAQ&biw=1920&bih=1115

Bosch has a special ABS check toolbox that is connected directly instead of the ecu unit.
Power on and testing can happen.

https://www.google.fi/search?q=rare+series+1+bosch+abs+testing+unit&source=lnms&tbm=isch&sa=X&ei=rtGOU8q4IKWI7Aa53IHwDQ&ved=0CAYQ_AUoAQ&biw=1730&bih=915#q=ledtester+bosch+II&tbm=isch

short track DIY testing:
abs ecu has pin rows
1 ... 18
19 ... 35

- open the cover screws for the connector comb to locate the sensor wire pairs
- electronic wiring chart has the 35 pin connector described as X1, sensors are described as X2 X3 X4 X5

VL = vorn links = front left
VR = vorn rechts = front right
HL = hinten links = rear left
HR = hinten rechts = rear right

ABS sensor cables are as cable pairs to following points. If you open the comb you can spot the 4 x cable
pairs easily in case there is a mistake in the drawing. Sensor cables are not built by BOSCH.

Also the cable extension connectors for rear are under seat and easy to spot for quick resitance check.
In my old series ABS unit electronic wiring chart for A80q there was a documentation mistake.
These were the correct as pairs

VL 22, 4
VR 11, 21 (was documented wrong as 23, 21)
HL 8, 9
HR 24, 26

my measured resistance values:
VL 0,96 kohm
VR 0,95 kohm
HL 200 kohm - way outside the accepted range
HR 1,19 kohm

accepted value range is 600 - 1600 ohm

front axle has 96 teeth and rear 45 teet => might be the reason why rear amplitude is smaller

Bosh led tester revealed:
In passenger side front the signal amplitude is much lower than on driver side.
interesting finding is that the rear values are much lower than the front values.
I assume that L-R balance is more important than front-rear signal amplitude balance.
Assumption can be wrong! I will first fix the rear sensor and then drive test again.
Drive test reveals soft "spongy" pedal feel (sudden drop of line pressure and soft feel on the pedal) in
the latest moment 2 meters before the car finally stops.

Unfortunately the factory warranty is over