Problems with the sensors that control automatic header height control systems on soybean platforms and corn heads can be a challenge to diagnose. If you are mechanically competent, relatively fearless, and willing to accept responsibility if you make things worse instead of better, here are some things you can do to diagnose problems with that system.
"DUH!" STATEMENT: DO NOT WORK ON ANY HEADER HEIGHT SENSOR WITH THE COMBINE RUNNING OR WITHOUT THE HEADER SAFETY STOP IN PLACE. (SENSORS SHOULD HAVE ADEQUATE VOLTAGE FOR TESTING PURPOSES WITH ENGINE OFF AND THE KEY SWITCH IN THE "ON" POSITION.)
-First, determine which sensor is causing the problem. It can be tricky, because there are two or three sensors, maybe four sensors, on a large header. Raise and lower the header, tilt the header if it has that capability, and decide which sensors are working, and which aren't.
-If you don't have a voltmeter, switch one of the "good" sensors with the questionable sensor. See if the header behaves differently. If the problem follows the sensor, replace that sensor.
-If the problem doesn't follow the sensor, be suspicious there is damage to the wiring harness leading to that sensor mount. Manually trace each wire from the sensor all the way back to the combine's main connector.
-Make sure the sensor mounting bracket and linkages aren't bent or damaged. Sensor brackets on some soybean platforms extend outside the side frame and are susceptible to getting bent.
-If you're comfortable using a voltmeter, it's possible to backprobe wiring connectors where they attach to sensors. If you don't know what wires are supposed to have what voltage, probe "good" sensors and figure out which wire is ground (usually black), which wire is power (sometimes red, but not necessarily) and which wire is signal. Then check to see if similar voltages are present at the sensor in question. If proper voltages are present in the correct wires, replace the sensor. If voltages are absent, check the wiring to the sensor. Be aware that some sensors can have "dead" spots as their sensing mechanism rotates or swings through its range of travel. Voltage (in a powered-up) sensor, or ohms of resistance (in an un-powered sensor) should increase or decrease steadily, with no skips or blank spots. Replace sensors with skips or blank spots.
Beyond simple problems with sensors, there is a world of complicated, potentially expensive, problems related to automatic header height control systems. But your problem could be something simple, something relatively easy to diagnose, so don't panic until it's absolutely necessary. Stay calm and check the simple stuff first. If the entire system quit working, check for a blown fuse or a main wiring connector that isn't completely connected.
There will be plenty of time for complicated, expensive diagnostics and repairs--and panic--after you've checked the simple stuff.