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A couple years ago when I had my C5 I had the same codes and problems. I looked at replacing the unit as per the instructions on this board. Out of curiosity though I tried one last fix before going that route. I had the brake lines drained and the replaced all of the break fluid. Not sure when/if that had been done in the past but it solved my problem. No more codes and no more warning about the EBCM problem. Relatively inexpensive/simple thing to consider.
You didn't happen to notice if there was trace damage or a ripped out through hole plating on the circuit board? I have no idea if it's possible, but I have seen other circuits were the through hole plating was ripped out and that caused the circuit to only be connected on the soldering side while the trace on the component side was left unconnected.
If you can clear the code with it running and it stays cleared then I'd try activating the ABS or jacking the rear up and running it in gear to activate the TC. Get the system actually working for a bit.
Thanks Neil and Lionel
I have the module off and will check the soldering. I have a vacuum tool and will pull clean brake fluid to each wheel. If I can get the c1218 to clear will cycle the abs by spinning the wheels.