I've put in a new air pump, and a new relay control module... no luck... the F2/engine control fuse on the relay control module keeps burning out after I start the car... The CEL only goes away the first time I start the car, which is probably when the fuse gets blown; the second time I turn it on, the fuse is blown, so the CEL comes back. I guess its off to the dealership...

US Auto Parts - Catalogs - 2004 Mercedes Benz SLK320 Air Pump Stock Replacement

MERCEDES-BENZ RELAY (170-545-03-05-05)