 The DEF system is working. Keep in mind, it's a good first test and it's a good maintenance test if you're changing filters on this yourself to keep these test strips around because if you ever see signs of petroleum, you want to deal with it right away because there are cases, Ford says, if you get any petroleum in that system, any sign of it with a test strip, you're changing. They want you to change the entire DEF system, which obviously gets expensive. Now, that being said...