Brake ECU

[studley07]

Hi I have a1990 Quattro Coupe 7a engine 2.3 20v. anyway having issues with ABS. light would come on then go out and stay out then sometimes it would flicker on and off and now its just on. took it to a garage I trust but they where unable to get any kind of reading from it. Maybe the brake ECU has let go. Anyway where is it situated on the car so I can get apart number and see if I can get one, any one had any kind of dealings with the same issue

[trebormc]

Hi mate the abs ecu is under the back seat, you may need to undo the two screws and lift the seat up.

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[newsh]

It’s probably a dirty wheel sensor or toothed ring.

[steve briance]

Tom has a thread running at the moment about his ABS woes. It's a lengthy read but the upshot is, his problems seem to be caused by earth stud broken off in the pump...

[steve briance]

I've had very few abs problems on.mine over the last 16 years but those I have had are all sensor related. The most recent was where the cable on n/s/R sensor had rubbed against inside edge of tire and worn through. Not sure how it managed to touch the tire.bit it did and it was obvious what was going on. Other faults had been internal failure of sensor which showed up easily by doing checks with multi meter for resistance and continuity. Be warned though, every time I've had cause to take a sensor out, it has needed digging, drilling, chiselling out due to corrosion.

[M2ki]

These old ABS ECU's need special tool read for diagnostic from them, vagcom and vcds are no go.
As you mentioned in the other thread that you changed the combi relay. Remove it and bridge the connector with a piece of wire.