MX5800 dies when rocking pedal forward or reverse (SOLVED)

Worksmart · Mar 3, 2025

MX5800 starts fine. Can be standing next to it or sitting on seat to start it. As soon as you rock the pedal to go forward or reverse, the engine cuts out. It will also quit when you turn on the PTO. Always restarts just fine. We've thrown a seat sensor at it and the pedal sensor found up under the dash. Neither part solved problem.

What part should we throw at it next? Trying to avoid loading on trailer and having it sit at the dealer for a month.

Thanks much

ptsg · Mar 3, 2025

I would revisit the seat switch. The seat might not be pressing hard enough on the switch to let it operate as it should.

Worksmart · Mar 3, 2025

We will definitely double check the seat switch activation but the question becomes why does it quit when you turn on the PTO? We've always been able to turn on the PTO either seated or when standing next to the tractor to start the feed grinder. To me that means the seat switch would not have to do with that situation.

You can be on the seat and rock the pedal or start the PTO and it cuts out.

thclimer · Mar 3, 2025

Does your parking brake have to be on if you are not in your seat and be able to run your PTO?

Do you have an electrical schematic for your MX5800?

I'm wondering if there is something other than just safety switches (PTO, Seat, Parking Brake...) more like a module which has failed but still allows you to start but not move or engage the PTO?

Worksmart · Mar 3, 2025

thclimer said:
Does your parking brake have to be on if you are not in your seat and be able to run your PTO?

Do you have an electrical schematic for your MX5800?

I'm wondering if there is something other than just safety switches (PTO, Seat, Parking Brake...) more like a module which has failed but still allows you to start but not move or engage the PTO?

No, the parking brake does not have to be on to run the PTO.

No electrical diagrams. Just using parts diagrams to trace parts.

I was in fact starting to wonder if it is a possible failure in the ECU. All of the safety components meet at the ECU as best I can tell looking the the wiring harnesses on the parts diagrams. There doesn't appear to be any real mechanical linkages for the safety components.

thclimer · Mar 3, 2025

Is this the sequence you have to use the PTO if your not in the seat:

thclimer · Mar 3, 2025

I'm having a hard time believing your ECU has failed for just this "safety" issue, that would be very unfortunate.

Hopefully someone with more familiarity about your tractor can help.

Worksmart · Mar 3, 2025

Thanks for the PTO sequence diagram. The thing is with this tractor we've always been able to simply start the tractor and then the PTO standing next to it. No parking brake needed. No flipping the seat forward. We run both a feed grinder and a hay bale elevator from the PTO. The tractor was purchased used and there is no sign anyone bypassed any safety features.

I hope it isn't the ECU because it ain't cheap. That's for sure.

thclimer · Mar 3, 2025

That sure does seem strange that something has changed with how you used to be able to operate your PTO and especially now you can not move the tractor without it shutting off.

thclimer · Mar 3, 2025

Is your seat switch just a simple switch? If so I'd just connect the wires together.

Can you follow the seat switch wiring to make sure its not damage or chewed?

Is there any sensor/switch that lets the tractor know that the seat is flipped up as is described in the PTO sequence?

Cycledude · Mar 3, 2025

I don’t own a Kubota tractor but on my LS if your not sitting in the seat the transmission needs to be in neutral and parking brake applied in order to start the engine. Also if your not sitting on the seat the PTO won’t turn on unless transmission is In neutral and parking brake is applied. Maybe it works different on Kubota.

Chewwy · Mar 3, 2025

Worksmart said:
MX5800 starts fine. Can be standing next to it or sitting on seat to start it. As soon as you rock the pedal to go forward or reverse, the engine cuts out. It will also quit when you turn on the PTO. Always restarts just fine. We've thrown a seat sensor at it and the pedal sensor found up under the dash. Neither part solved problem.

What part should we throw at it next? Trying to avoid loading on trailer and having it sit at the dealer for a month.

Thanks much

Could be a fuel flow issue. Check the fuel filter. Had similar issue with my L3240, didn’t stall but was greatly under powered when trying to increase speed or climb a hill. Fuel filter had a waxy substance in it. Replaced fuel filter, problem solved

JWR · Mar 3, 2025

Chewwy said:
Could be a fuel flow issue. Check the fuel filter. Had similar issue with my L3240, didn’t stall but was greatly under powered when trying to increase speed or climb a hill. Fuel filter had a waxy substance in it. Replaced fuel filter, problem solved

No. There is no fuel related issue that would allow starting and running the engine and then it be forced to shut down when you attempt tractor motion or to run the PTO. Chewwy you had a very different problem.

rScotty · Mar 3, 2025

Worksmart said:
Thanks for the PTO sequence diagram. The thing is with this tractor we've always been able to simply start the tractor and then the PTO standing next to it. No parking brake needed. No flipping the seat forward. We run both a feed grinder and a hay bale elevator from the PTO. The tractor was purchased used and there is no sign anyone bypassed any safety features.

I hope it isn't the ECU because it ain't cheap. That's for sure.

I'm betting it is one of the switch adjustments. On our Kubota M59, there are times when I can start the engine with the seat reversed and the hand brake off....and times when it wont crank unless the hand brake is on and the seat "reset" as well.

It doesn't make sense to me....but somehow the way that the ECU views the switch positions seems to have changed over the years, and I'm not sure why.

Last time it happened - last summer - I went through all the safety switches and carefully set their free play and engagement clearance, then pulled all the fuses and cleaned their contacts.
That seems to have worked. Now it works the same as it did when new.
But I'll admit that I have no idea why.....

Kubota Red · Mar 4, 2025

Seat switch (and it's circuit) is the only one that will kill the tractor when the pedal is pressed or the pto is turned on. Try starting it, tilting the seat forward and engaging the pto (the switch is designed to allow the pto to run if the seat is tilted forward). I have never heard of an issue like you described being an ecu problem. Most likely the switch (bad, damaged, misadjusted, etc.) and second would be the wiring harness.

Worksmart · Mar 6, 2025

Kubota Red said:
Seat switch (and it's circuit) is the only one that will kill the tractor when the pedal is pressed or the pto is turned on. Try starting it, tilting the seat forward and engaging the pto (the switch is designed to allow the pto to run if the seat is tilted forward). I have never heard of an issue like you described being an ecu problem. Most likely the switch (bad, damaged, misadjusted, etc.) and second would be the wiring harness.

Thanks for this. I did exactly as you suggested and tipped the seat forward and got the PTO to work without killing the engine.

After that I really started looking hard at the seat switch and wiring. Lo and behold I found the broken(orange) wire. It was very hard to find as it was tight up against the connector on the end of the wiring harness. Hidden just inside the ribbed loom protector and some tape. Surprised we didn't catch it when we changed the seat switch a few days ago.

Thanks to all who chimed in!!