09 Toyota Camry 换机油后灯亮了．（maintenance request）换前倒不亮．

I changed oil and filter last weekend in a Car station. The miles was 35228.00 at that time,

This time the “ maintenance request “ light wasn’t on before changing oil , but it suddenly showed on this morning. I remember this kind of problem happened before and I brought the car went  to the station and they said “ no problem” and just pushed and turned it off. I think they will do it again but like to know why ? 这个灯是连着一个sensor 还是就是一个机械的装置，每５000 miles 亮一次？要是后者就是车铺忘了关上，要是前者就难说了,说明还有别的问题．