PRoj

I have a 2003 CL55 AMG,,,i suddenly lost my power steering. No grinding, no whining or the usual precursors to a part failure. i am new to this vehicle. When i pull the reservoir cover off with the engine running, the fluid is still, no movement. Is there any sensor or code that would turn that section of the pump off? I know uts a tandem pump that incorporates the pump for the struts. The struts where replaced and the ride system raises and lowers properly. There is an ABC code on the dash monitor. I just do not want to buy a new pump and replace it if that is not the problem. Can anyone advise me how to find out for sure if the pump needs to be replaced? Thank you