Tip for NX-Series Owners: Mysterious starting problem solved

[Threepoint]

I'm posting this in the hopes it might save another NX-series owner some of the head scratching I went through recently with a mysterious starting problem that turned out to have a very simple, but surprising explanation. Apologies for the length, but I thought of some TBN'rs might find the step-by-step description interesting.

Recently my NX4510HST wouldn't turn over with the key switch turned to Start. This, after 2-1/2 yrs of instant starts, every time, in all conditions.
With the key switch simply in the "On" position, I'd hear two relays engage and all dash lights would illuminate.

So I ran through the first usual steps to trouble shoot: Butt firmly in seat; transmission range selector in Neutral, PTO switch off; Parking brake firmly on and parking brake dash light illuminated. I also checked to see if voltage was getting to the main terminal of the starter solenoid. Yes, a healthy 12.7 v.

But there was no voltage getting to the solenoid's Control terminal with key switch to Start. When I bridged between the solenoid's Main and Control terminals with the key switch in the On position, the tractor fired right up and would run normally until I shut it off.

I next removed and tested the 70A starter relay that is mounted on the firewall (not the starter solenoid itself, which is attached to the starter motor). The relay tested fine.

I also tugged on the harnesses that I could easily reach under the hood, but found nothing loose. While sitting in the seat, I checked the seat safety switch for continuity and it was fine. I checked to make sure the PTO dash light was on when the PTO was engaged and off when it was not. I tugged at the wiring connection at the HST range selector switch (up under the left rear fender), and it was not loose.

So, I reluctantly began to suspect an ECU issue.

The Kioti workshop manual says the following:

"When turning the key in the main switch to the "ST" position to run the start motor in order to start the engine, power from the battery is passed through the main switch and terminal ST and is led to the terminal No. 212 (ignition witch) of the ECU. When the ECU receives a ST signal, it sends a "-" signal to the starter relay No. 237 [of the ECU] to activate the starter relay. Then, as the starter relay contact is connected, battery power is directly delivered to the start motor from the slow-blow fuse (main, 60A) to start the engine."

So it was pretty clear in my situation that the ECU was either not getting or not processing correctly the signals necessary to allow power to get to the starter solenoid Control terminal. At that point, I decided the solution was beyond my abilities. Since my tractor was due for a Kioti ECU programming update, and I had been planning anyway to add a third set of rear remotes and a W.R. Long electric-over-hydraulic 3rd function to operate a grapple, my dealer picked up the tractor and took it back to the shop.

The mystery finally solved

In going over the tractor, the dealer's tech noticed that the fuse to the brake light circuit was blown. He replaced, but it blew again. After more investigation, he discovered that a wire in the right rear brake light housing had chaffed its insulation and was grounding out. Once he taped that up, the fuse held, and the tractor started right up!!

So here's what we learned from all this: On the NX series, the tractor's brake light circuit must be fully operational in order to signal the ECU's terminal No. 237 ("starter relay") to complete the starter relay's primary (control) circuit. What was throwing me off is that the parking brake light on the dash is not part of the regular brake light circuit. So, even though the parking brake was firmly on and the indicator light on the dash illuminated, the ECU still thought the safety condition had not been satisfied and would not allow the tractor to start.

So my tractor is starting reliably again, my ECU has been programmed with the emissions update, and my third set of rear remotes and electric over hydraulic 3rd function are installed. While he was inside the tractor, I also had the tech run an additional lighting circuit and install a factory rocker switch for a third pair of LED work lights that I've mounted to project on either side of the tractor.

Much appreciation to the guys and gals at my dealer, Tractor Hill Equipment, in Mineral, VA, and especially to their excellent tech, David, for taking care of me on all this.

 

[murphy1244]

Good news and a fine write up. Thanks.

 

[rhunt]

Great write-up! Good info! Bob

 

[Hope Caper]

I don't run a NX but your problem was interesting and your resolution unique to say the least. Great read and a lesson to the rest of us-- the devil is in the details.

 

[kromc5]

Thank you very much for the time to write this, I will print this and put in my manual for safe keeping.

 

[DieselBound]

I wonder how many people have hurt themselves trying to resolve "safety" (interlock) features?

I don't own one of these tractors (yet; I'm researching on various failure issues to know whether I'll be OK with one of these) so I'm unsure about all the interlock stuff. Do you have to step on the brakes in order to start? I test drove an NX4510 and don't recall noting this: it's kind of instinctive anyways for me to hold down on the brakes when starting. Just kind of wondering if one wasn't stepping on the brakes whether this problem would have still been there (assuming, of course, that brakes aren't part of the safety interlock circuit).

Great writeup. Hopefully Kioti alters their harness/wiring to reduce this possibility. (and then to be really paranoid, wire looms themselves will, over time, chafe the very wires they're supposed to protect; and, you won't see it- you'll have to peel everything back.

 

[countrybumpkin]

Yes you have to apply the brakes to start the nx

 

[DieselBound]

Yes you have to apply the brakes to start the nx

OK, then that explains things.

Is there a display for system codes for problems?

The specific type of failure here might not have been something expected, but it seems like the ECU's programming was handling it, recognizing something in the interlock logic wasn't setting correctly. Seems that with all the interlock switches and such I'd think that having something inform you that that's the problem would go a long way to helping folks get things going again.

 

[Threepoint]

Yes you have to apply the brakes to start the nx

Yup. Or set the "parking brake", which accomplishes the same thing. The starting sequence in the owner's manual actually begins with "Make sure the parking brake is set." To set the parking brake, the two brake pedals must be interlocked, then held down while the parking brake lever is pulled to set it. Then the parking brake indicator light on the dash illuminates.

As a short cut, you can just hold both brake pedals down with your foot without engaging the parking brake lever and illuminating the light. So turns out that the "parking brake" is actually just the regular brakes being engaged and the lever set to hold them on.

So it further turns out that the brake-related electrical signal that the ECU looks for as a precondition to starting comes from powering the brake light circuit (by engaging the brakes), not from the circuit powering the parking brake dash light. This is what was throwing me off.

DieselBound, yes there are six error codes that display for certain conditions in the LCD window for the hour meter on the dash. My problem unfortunately wasn't one of them. :laughing:

One thing I don't know is whether an error code reader can be plugged in by the dealer for more, and more detailed, info. Maybe Eric, Country or another NX owner knows. I didn't think to ask the tech, although he found the problem the old fashioned way: by trial and error, including checking all the fuses and replacing the brake light fuse a couple of times before discovering where the short was.

 

[DieselBound]

I've got some older TDI VWs with ECUs and am fairly versed in running diagnostic software on them. But, like you note here, not everything will throw a code. Really seems, however, that there really should be some status signal, dash light or such, that will tell you if you have all the interlocks reporting they're ready for a start- this sounds kind of dumb, in that if everything is working then you should be able to start, but I still think that some sort of feedback that signals OK might be a good idea (or maybe it would be just another thing to fail and cause confusion?)

I was thrown for a big loop on my B7800. I'd been mowing and the seat rails broke on me: I've been tossed around REALLY hard on that thing. I had to continue mowing so I tossed off the seat and continued (not comfortable at all, but that's how I roll). After some time the tractor just flat out stopped. I was sure the seat interlock/safety was the problem. I jumpered everything but still no go. First time ever I had a blown fuse AND the relay wire on the starter got knocked off. So, yeah, there's really no substitute for good old-fashioned troubleshooting.