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The only person who I know who has successfully repaired any of these early EBCMs is Chuck Cow. As far as I know he will only repair them if you bring the car. Also, he can only repair the unit if it is a relay problem which is probably the most common mode failure in the units. A lot of companies say they can repair it and then when they get it they say sorry. I wish Cardone would take on this challenge.
I have a link at home on this and also the Bosch relay number if you want to try and do the relay replacement and see if that resolves your issue. With that being said there is one code (I think C1255) which is the DEATH CODE for the EBCM since it is a chip, software, or board related issue.
I will send you the link and info if you like. Not at home with the info now. Just respond to this post so I remember (I am old).
PS: I am an old school car guy. I don't need/want ABS, Traction Control, or Active Handling. I always turn TC off which also defeats AH. Can't turn off ABS but if it does not work, normal braking is still retained. I prefer to be in control of my car not some gizmo that can fail with some surprising lane change attributes which has been well documented. If I have traction issues that is why the steering wheel and throttle are there. If I can power drive a high performance mid engine car through a high speed curve and not kill myself (yet), driving the C5 without the stuff is like "Driving Miss Daisy" around.
The on-board ECU is the problem with these. What I've found is that Bosch supplied the mechanical/hydraulic and Delco installed a dedicated ECU board. Finding the source of these boards would be a lot of help for a lot of folks. I was jst asking if there was any experience with this vendor regarding this.
Whether you can live without ABS is a personal preference until you get to a state safety inspection. If they pull codes and you have abs failure, no tickee no shirtee. There are some other drivers out there on the same street with us, and they need all the help they can get. They dont have a flag on their antenna so you know when they are approaching.