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[MonzaGSE]

Have had ABS light on for a while now. Was diagnosed at Opel with most likely failed central unit. ABS light would go out after startup and then come on again after the car had moved just a few meters. On closer inspection there was a leak from the servo steering hoses which ended up on the ABS unit. Took the ecu out and found it to show several signs of moisture/corrosion inside.
Ordered a used ABS complete ecu/pump unit from eBay. Numbers on the unit and on the ecu matched. However the new unit came from a a 95 2,5td.
I have just changed the ecu, not the pump and valve unit. On initial startup ABS light went out and came on after a while as before. After that the ABS light just stays on all the time and never goes out.
Will the new ecu need a tech2 since it came from a different engine? Looks identical to the old one.

[Doctor Gollum]

It could also be faulty... Need the codes from it, if possible at that age. May not even be the ecu... 

[MonzaGSE]

Fault code 35 pump motor relay circuit. That was the code when original ecu was fitted. Will take it back to Opel i guess and see if they can program correct engine/gearbox. And get current fault code if programming dont solve it. Next step would be to change the pump also. But had hoped to avoid that.

[Doctor Gollum]

Minimal extra labour if you add it to a fluid change

[TheBoy]

The early ABS units are generic bomb proof with the exception that a relay can stick on the non TC variants - if you get this, 9 times out of 10, a good tap on the unit cures it for a decent period.

Not sure if the early ones are programmable, I've never known anyone have to change one

[cam.in.head]

probably already been checked and sorry if stating the obvious but had a similar problem years ago on a series 3 carlton.
light came on and went out on startup as normal but came on when you started moving.
everything was checked by a garage and the abs unit was swapped but problem remained.
we also checked sensor resistances,mounting positions,wiring etc,
turned out to be rust particles from corroded front disc shield jamming up the slots on the toothed wheel. pickup then interpreted this as a speed error !
other things to check are,diferent sized tyres,loose toothed wheel (rear i think),mixed up connectors( left,right)
probably wont be any of these things but just passing on info !   may be of some help

[deviator]

I'll add tyre pressures, cracked ABS ring to the list above.

[MonzaGSE]

Did check rear sensors and cleaned up rear rings. Front sensors are stuck so i dont think i can get them out without destroying them. Anyway i went to Opel again today. They erased error codes testdrove the car and checked what code reappeared. They got error code on the hydraulic valve block. They believe one of the valves are stuck. Got a used valve/pump unit that is supposed to be in good condition. Plan on swapping it in during christmas and hope that solves the issues.

[cam.in.head]

eassiest way ( probably the only way ) to clean / check the fronts if you can get in behind the disc shield is to just whip the hubs off. but it sounds like you may have identified your issue anyway.
mine was a front hub issue but never had it on a reader just found and cleaned up the mess and all was well .this was a few years back .around 97 ish on a 89 carlton .

[MonzaGSE]

Update: Finally resolved. This Omega has been left in the garage for a while now since the temperatures have been -15 to -20 celsius for a month now. The other Omega 2,0 has been running fine the whole time, and the 95 mv6 Omega backup vehicle has also been in daily use again.
Finally took a new look on this yesterday as the weather dont seem likely to get warmer any time soon. Anyway, installed ABS ecu nr 3 and suddenly all seems fine. Light went out and can feel ABS working when braking hard on the snow covered yard. Original ecu had corrosion inside, ecu nr 2 came from a 2,5td and was obviously either wrong type or faulty. Nr 3 came from a 94 2,0 and all was fine:)

[Doctor Gollum]

Bish, bash, bosh