Steam cleaners are very bad to use, infact I've heard from sountless amounts of people that you should not use a steam cleaner for the reason listed above, and the steam will mess up some electronics.
Just spraying and hosing it off with simple green wont work, and neither will a pressure washer alone. Sure the pressure washer will get the dirt off, but if its oily/greasy then you'll have to scrub it with a degreaser. No easy way around it