750il Anti lock and ABS

My anti lock brakes and ABS Quit working a year ago on my 8/90 750il US

Here is what is going on:

Anti Lock lite is lit on the dash . . . once in a while if I hit a bump or sometimes for no reason the heads up display will read ASC not active

At the very begining it would go out after restart or would go on and off at speed ( 60 +)

Here is what we have done to try to fix this nightmare.

Pin out of all ABS Senors checked out ok

Dealer computer readout on system does not work on 1990. (first year of this system)

Cleaned Tone rings on rear axle. got them pretty clean

Replaced one ABS sensor ( but machanic told me he knew it would not do anything ) No charge.

Swapped out ABS control panel on a working 750 ( this is the unit on the passenger side engine compartment under the big black case)

Any thoughts out there thanks

-- ABS problem: Are you telling me that the BMW dealer cannot read the codes for a 1990 750iL? Time to find a better dealer! Call and schedule an appointment with another BMW dealer, in another town if necessary. I mean, this is your BRAKES we're talking about. Better yet, if you're in the US, call BMWNA at 1-800-831-1117. Maybe they can guide your local mechanic through the steps to find the problem.

-- Also, there's the "stomp" method to have Mr. Computer blink the codes to you via the Check Engine Soon light. Here's a link about how to do that:
http://www.pelicanparts.com/bmw/techarticles/Mult-Code_Reading/Mult-Code_Reading.htm

-- "Swapped out ABS control panel on a working 750". You didn't state the results but I assume the light stayed on. Remember, the light means that Dr. Computer "thinks" there is something wrong with your ABS system, and in your case, Dr. Computer #2 concurs, so Dr. Computer himself is probably OK.

-- "once in a while if I hit a bump or sometimes for no reason the heads up display will read ASC not active". This might be normal. I've seen it happen on my car (and on my van) if you turn in somewhere that has a bit of a rough entrance. One wheel looses traction for a fraction of a second and the system thinks it's in the snow or something. Again, this indicates Dr. Computer is alive and well.

-- Last but not least, there's lots of help at www.roadfly.org.

I was traveling all weekend and when it got hot outside ( Over 80) F the ABS not active message came on. so you are correct the ABS DR computer is alive and well. It is the Anti lock system that is the problem.

I am beginning to think that it may be the hiring harness or a ground strap problem. I need to look through my bentley book and see where the wiring harness is located.

I am leaning toward the ground strap is that my variable assist power steering sometimes works and sometimes is weak. That can be caused by a faulty ground.

I also have the BMP fault code reader.

I comes up with a fashing E for Comminication error. I have followed the directions from the web page and got it to work once and I came up with no faults. which I know is not correct.