JD870 Will Not Start

[TedLaRue]

NWL,

In the nutshell, here's how your starting system for you John Deere 870 works. The safety switches (PTO switch, seat switch, and transmission-in-neutral switch and (if you have one) mid-mount PTO switch) all feed into the Time Delay Control Module (TDCM) which is the large black plastic box which is on the right side of the attached picture. There is a black w/red stripe wire connecting the TDCM to the Neutral Start Relay which has the red arrow pointing to it in the picture.

Check for voltage on that black w/red stripe wire when the switch is in the cranking position. If you have voltage on that wire when you're trying to crank the engine, but no voltage on the white wire from the Neutral Start Relay to the starter, then that relay is bad. You might try rapping it with a screwdriver handle while you're trying to crank the engine in case it's just stuck.

If that red/black wire doesn't have voltage on it when you're trying to crank the engine, then you need to check the TDCM. Let me know if you want some guidance checking that.

 

[TedLaRue]

NWL,

Here's something else that's really easy to check. Make sure the black plug that plugs into the white receptacle on the bottom side of the Neutral Start Relay (the one with the red arrow in the picture in my previous post) is plugged in tight. I was messing with mine when I took that picture, and had partly pulled that plug out. When I got on my tractor to start it, I had exactly the same symptoms you described. Wouldn't that be a nice resolution to your problem!

 

[NWL]

Update: I got to a point that was beyond my basic knowledge, and because of the amount of time it would take to get up to speed, I bailed and got hold of a mechanic to come and look at the tractor ( not an easy feat in our little neck of the woods!). He went through the same procedures outlined above by TedLaRue, and ended up at the seat switch. Power was going to the switch, but it was not receiving it (fuse was good). The thought is the seat switch went bad, which is what the JD service tech believed was the last thing to check before he ran out of ideas. So I'll replace the switch, which will take a few days as the dealer is 70 miles away and I'll need it sent to me, but I will post an update on the result for future reference.

Thanks again to everyone who posted their ideas.

 

[NWL]

Latest Update: I really wanted an easy fix to my problem, but it was not to be. I replaced the seat switch but the tractor still will not turn over. I went back to TedLaRue's instructions for checking the Neutral Start Relay and I did it right this time. There is no voltage on the black w/red stripe wire when cranking the engine. I'm awaiting further instructions from him (bless his heart!) on how to check the Time Delay Control Module. I'll post the results soon.

Thanks to all who have posted.

 

[TedLaRue]

NWL,
Does your tractor have a mid-mount PTO? If not, look on the left side of the back of the tractor, close to the transmission/hydraulic oil dipstick. You should be able to see two wires going to the rear PTO safety switch mounted on the side of the transmission case. Close by you should see a couple of single-wire connectors with a short piece of wire between them. That wire is a substitute for the mid-PTO switch. If something caught on that wire and pulled it loose, your tractor wouldn't start.

For the TCDM (time control delay module), there's a short wad of wires coming out the bottom, and then a connector. You can test voltages at that connector.

With the key in the crank position, you should have 12V on the Blue/Yellow wire and the Blue/Red wire.

If no voltage on the Blue/Yellow wire, try again with the seat switch in the "defeat" position (i.e., tilt the seat forward and pull up on the switch). This removes the PTO switch(es) from the mix, leaving only the transmission-in-neutral switch.

Depending on your results, you'd need to check out the transmission-in-neutral switch or the PTO safety switch. There are several combinations of those switches and the seat switch here, and there is also the "old version" and the "new version" of the wiring which involves those switches, so I'll stop providing speculative choices until you post back.

 

[NWL]

SUCCESS!!!!!! It finally starts. In a nutshell, here's what happened since my last post: Once we determined there was no voltage on the black w/red stripe wire on the Neutral Start Relay, TedLaRue sent instructions for testing the Time Delay Control Module as well as instructions for checking the "dummy" connector for the mid PTO (my 870 has no mid PTO). I disconnected, cleaned, and reconnected the "dummy" connector for the mid PTO while my husband disconnected, cleaned, and reconnected the connector for the TDCM. He went off to get the voltage meter, and I, just for yucks, decided to get on and see if it would start. Scared the you-know-what out of me when it started right up! So one or both of those connectors needed cleaning and/or one or both were loose and needed to be secured.

My thanks to all who posted there ideas. I learned a lot through this ordeal! See you on the forum!

 

[wairon]

I am diagnosing this same problem. Great info.

Thanks

 

[NWL]

I am diagnosing this same problem. Great info.

Thanks

Welcome to the forum! Yep, this is a great resource. I'm glad you found the thread and hope it is useful. TedLarue is great and is very knowledgeable and helpful. Send him a private message if you need further instructions.

Cheers!

 

[wallfarmer]

had same problem on 4300, all I had to do was wiggle the wires going to the nuetral switch and all was well. They really crammed that switch under the floor platform on the 4300 and the wires get pushed on by the platform.

 

[stuckinarut]

Hello, I am a new member here and am glad to have found this great source of info. Thanks to all those that take the time to help others!

I am having the same trouble getting my 870 to crank over, new battery and cables, I tested the TDCM wires as advised by TedLaRue above. I get 12V from the blue and yellow wire and only .75V from the blue and red wire coming from the TDCM when the key is held in the start position. Any advise on where to go from here is appreciated. Is the TDCM toast?