EPS issues on Z4 E85 : my personal experience, hope this could help some E85 owners.
Hi,
I had an EPS issue 2 years ago. No power steering at all, error light of EPS ON on dashboard (permanently). After diagnose, there was no communication with eps ecu : I made it fixed by a specialized ECU-repair service.
It worked perfect 3 month ago.
After this I had intermittent issues (no power steering , intermittent error light shining). Diagnose was : "low voltage". So I tested voltage and ground at the electric motor of the EPS,tested alternator voltage, battery and it was ok. I decided to go further to have a good electric circuitry and I cleaned all the ground points (on the body of the car).
Problem disappeared for more than 36 month.
After this, I had intermittent issues again (No power steering and error light of EPS error shining), and the steering was "floating" on all kind of roads... But no EPS failure on electronic diagnose. I decided to verify the front suspension triangle because of the strange behaviour of the car. The right side silent bloc was in a very bad condition... I replaced both silent blocs : EPS issue disappeared now, the steering behaviour of the car is now fine as well.
I think that the strange behaviour of the right suspension gave strange information to DSC (dynamic stability control) via the DSC captor situated on the right suspension triangle and gave probably that error. It is important to know that DSC, ABS and EPS are influencing each other.
So, before changing an entire steering column by a new expensive one, be sure everything is in perfect mechanical and electrical condition everywhere else. Make a good electronic diagnose and read the codes.
If you need some WDS or other diagrams or photographs concerning those issues, I can provide them.
Philippe