The only way to do it that I know of is to pull up on the fender (be very careful not to pull in a place that could rip things off) and have a friend put a finger on the top of the strut mount...if there is a popping feel or a popping sound when the struts are lifted up and down, up and down then they're blown or defective. That's how I finally figured I had a blown one after 2 painful months of listening to a knocking noise in my suspension.