People often take a “set it and forget it” mentality towards there sprinkler system. By the time they figure out something is wrong, there is a HUGE brown spot in the middle of the lawn.
It is a good practice to check your sprinkler system once a month. An easy way to remember is to do it when you get your water bill for. Make sure your entire lawn is getting wet. You should also be getting head to head coverage.
Lawns will also need more or less water at different times of the year. Make sure you are adjusting your time and frequency according to how hot or wet it has been.