Fixing a John Deere Gator Starting Issue - Troubleshooting Steps

My John Deere Gator 850d diesel decided to give me some attitude and refused to start.
It took me a while to figure it out, but in the process I think I checked every potential failure point that would result in a no crank situation.
The troubleshooting steps should be identical on a Gator 855d, Gator HPX, and very similar on gasoline gators and many farm tractors and offroad machines.
Hopefully this can be helpful to folks out there.
Tools used in this video:
- Power Probe 3 amzn.to/46Zm7gj
- Relay Bypass Tester amzn.to/3slpwa4
- JNC Power Brick amzn.to/3QkktyO
- Brake and Electrical Cleaner amzn.to/47fVwvm

[@EagleNestFarm]

As always, I found the issue and had a scary moment off-camera when the gator just started cranking for no reason, and with no way to stop it - haha. The ignition key was already off but the thing would keep cranking!!! It took me a few seconds to figure out that the relay bypass was actuating the starter and I turned it off. Pfew!

[@therapeuticridingoftucsont8644]

Great video. Exactly what’s happening with my 2012 hpx.

[@bogesmalone4514]

Having the same issue with my Xuv 550 s4. Im not sure where this relay switch is though on this model. Thanks for the video!

[@kennywellsiii2785]

Very clear and very helpful.

[@EagleNestFarm]

I am glad it was helpful and thank you for the note. Take care!

[@OldAcres8690]

Thanks for the help and knowledge.

[@EagleNestFarm]

Glad to be of help!

[@Ugot2BkddnMe]

My 825i has the same issue and that is why I'm here. Turn key, dash lights come on but engine does not crank. 1. Battery, 12.7 2. Checked fuses: all good. 3. Swapped ignition module - no change. Up next, relay check. then gear sensor. Starter was replaced , 6 months ago. UGH~~~

[@EagleNestFarm]

This is frustrating... I wish you good fortune with your troubleshooting! The gear sensor may be the easiest next step for you to check. Just spray the connectors with some brake cleaner to help make a better connection.

[@Ugot2BkddnMe]

@@EagleNestFarm arrgh~~ my quest to repair my gator continues. I replaced the starter and when I re-attached the battery I encountered the same issue I believe you mentioned. With the key in the "off" position the gator cranked and started. If I turned the key "on" then "off" it would turn off only if I disconnected the battery. Next... relay switch. did i say..AARRGGHHH~~~~

[@EagleNestFarm]

@@Ugot2BkddnMe Oh man. This sounds a little scary. Glad you figured out how to shut it down. Seems to me like a symptom of a malfunctioning starter relay. Good luck!