[torriem]

Chopper knives message is obviously unrelated. Usually what happens is the lever you move to engage or disengage the knives has bent a bit and isn't close enough to the sensor. You can bend it back. At least this message won't shut down the rotor for you, at least it didn't for us.

As for the other message, It's probably a wire that broken. Check the bundle of wires that goes down the left side of the feederhouse from the combine to plug that goes into the headers. Pull off the plastic loom material and look for wires with worn insulation. Over time the plastic loom will wear into the wires which can cause them to short to each other. that's the first thing to check. You can also go into diagnostics[1] and pull up the voltage for the header height sens and see what it reads. It should be low but not zero without a header on. As you go up and down see what it does. And you can have someone wiggle the harness while watching that.

[1] If I recall you go to diagnostics->settings and select the header height sensor, then switch to the graph tab to see the readout.