John Deere 4520 intermittent starting problem

[Trainpilot]

We have a 2014 4520 with about 1200 hours. It only starts intermittently. When it starts it runs fine. Whether it just cranks or starts, it shows an error 207 code. After 3 trips to the dealership asking about it, they figured out that the code indicates a fault with the engine position sensor. I changed the sensor on the front middle of the engine to no effect. (a $35.00 part) A JD tech came and hooked up a couple of black boxes to the tractor and could not figure out what the issue was. He said he would send the files to JD and that they would tell him what was wrong. Several days later, the service mgr informed me that the controller is bad ($2000.00 + labor). I have not yet given them the go ahead, but we're going to need the tractor soon. I'm wondering if anyone else has had a similar experience or has any good suggestions. 4120, 4320, 4520, 4720 are all in this series. CRD with a black box controlling everything. It tells you if you have a burned out tail light, but can't diagnose itself. The manual gives a very short list of error codes--as I mentioned, even a determined tech had trouble finding out what error 207 was. I have a good relationship with this dealership and have asked for some help vs the cost of the controller, as I think it was still under warranty when it failed.

 

[Wagtail]

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Because it's an intermittent fault I'd also suspect a 'sticky' relay (located in the fuse area). You could swap the relays around as they're usually the same type... but you may not know right away, due to the intermittent nature of the fault, if it has been solved. Purchasing a replacement relay (inexpensive) would be the way I'd go.

Vibration, especially with the amount of hours on your 4520, can cause the weirdest faults.