It's BEST to always remove negative terminal of the battery before you intend to do some sort of engine cleaning job. Plus, cover all relay boxes with plastic wrap and all sensors with tape/wrap as well. Once secured, use engine de-greaser to clean all the mess up and then let it dry in a properly ventilated area. Let it stay with engine hood open for a couple of hours to ensure everything is nice and dry. After that, pull off all the protection wraps and re-connect the battery. You don't need to do this often so it isn't a big deal to take the negative terminal of battery off because the ECU will learn everything again within 100 Km of driving (or even less). But if you fry something, that would be a pain.