I have a 1999 Mercedes SLK 230. Without removing the secondary air check valve how can I tell if it is functioning correctly? I removed the hose to it and when I run the engine I get some air coming out of it. With the engine off, the hose off and another longer hose in its place I get very little resistance when blowing air with my mouth. Finally how do I take this check valve off? Car is not rusted. I know there is a hex head below but there is no place to put a large wrench. Is there a specialty tool for this removal? I have read reports of people destroying the entire assembly trying to get these valves out. Thanks!

Is there a symptom that suggests a malfunction?