ECU stands for (Engine Control Unit), I found out how to take the ECU out so please disregard this question. I will try to upload pictures next week on the SLK350 forum, sorry to intrude on the SLK55 forum

. Its actually located under the air intake manifold, a very simple task, easier then I imagined, I was doing things the hard way, while Mercedes made it extremely easy. The ECU was staring me in the face the entire time. Its that middle silver rectangular shaped thing right in the middle of the Mercedes cover (in reality that cover is the air intake manifold).