when its green, the car is Ok....when its yellow, you are getting close to a mile mark, and when it is red, you are at/passed the mile mark, and need maintenance. Generally, it will change red every 7500 miles. Its just to remind you to do whatever maintenance is sceduled for that mark. If you tell me what mile mark you're at/approaching, I can tell you what needs to be done (as per my Helms manual).