Had to replace mine as they'd gunked up, as JRP says though open the bonnet and you'll see the pipes going into the jets, unplug them and try them. If you do remove or replace motors make sure you get them the right way round, as although they look the same one is more powerful than the other, when i first replaced them I couldn't get any jet at the front, and the rear washed the spoiler, so I swapped them.