Stuff, which You should check before harvest:
-calibrate automatic header height systems so that the header is talking correctly with the combine.
-if you’re using auto-steer, make sure all your GPS satellite subscriptions are up to date. The frequencies for some guidance systems were altered this summer. Most on-board systems were supposed to automatically make the frequency switch, but it wouldn’t hurt to make sure everything is working before you head to the field.
-clean the fuel/water bowl or filter on the combine engine. Combines frequently get their fuel tanks filled from portable fuel tanks, and portable fuel tanks are notorious for accumulating water and crud. Tier III, Interim Tier IV and Final Tier IV engines are incredibly sensitive to water in the fuel, so give them clean fuel and keep the water-catching filters clean.
-if you installed bigger or smaller tires and rims on the front or rear of the combine, be aware you may have to change several things on the combine, including the calibration value in the cornerpost display that calculates ground speed, and the tilt of the face-plate on the feeder house that determines the angle of the header to the ground. And if you added a grain tank extension–make sure it will clear the door of your machine shed, or the overhead wires in your barn yard.
(Based on – http://www.agweb.com/blog/in-the-shop/stuff-you-may-have-forgot-since-last-harvest/)