This is one of the few things Mitsubishi did in a way that does not make much sence.
The system assumes that you take the car in for service exactly at the mileage when the service icon shows up so instead of resetting to a set number (or 100% oil life like GM vehicles do) it adds the mileage for the next service...I don't even understand the thinking behind it but if you reset early,it will pile the miles on the display from where you were supposed to take it in...
We were talking about this at the dealership with a friend of mine who is a mitsu tech and he was telling me that at mitsu school/training that he went to,the instructor was trying to show them in class how easy it is to change the service intervals using the Mitsubishi diagnostic computer and after 15 minutes of punching the touchscreen on the tablet he said well,it's not taking it now... so they did not succeed.
The best thing is to go with mileage between oil changes and when the wrench comes up just clear the sucker and ignore the numbers displayed because it is a silly system they got going on for our cars.
On the Outlanders and some other models it is possible to change the intervals without having to hook up the Mitsu computer but it is some secret sequence of button pushes to enter that mode and in my opinion not worth the effort.
I go with a mileage sticker in the corner of my windshield because I trust that over any computer they ever invented.
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View my fuel log 2014 Mirage DE 1.2 manual: 66.3 mpg (US) ... 28.2 km/L ... 3.5 L/100 km ... 79.7 mpg (Imp)