L5740HSTC-3 ERROR-20 Help Please

RDubbs

New member

Equipment
L5740HSTC-3
Sep 8, 2024
6
5
3
Seven Valleys PA
Hi, I just purchased an L5740HSTC-3 with 1900hrs on it that the previous owner wasn't interested in trying to figure out. I was in need of a 50ish hp tractor for my small farm and the tractor was priced that even if I can't fix it, I can part it out or possibly even purchase a similar model and just keep this one for parts. I've confirmed the engine is ok, we pulled the stop solenoid and jumped the solenoid to the starter, the engine popped off right away, this made moving the tractor easier since we could move the loader and it made steering easier. I apologize for the lengthy post below, I'm just trying to give as much information as I can up front with regards to what I've tried so far. I will bold my actual questions.

When you try to start the tractor normally it throws an ERROR-20 code on the panel. I've purchased the WSM for the tractor it says this is a communication error between the ECU and the electronic instrument panel and the first step is to check the fuses, I assumed this is referencing fuse the 5amp T/M controller 1 and the 10amp T/M controller 2, both of these fuses are good and so are all the rest of the fuses. The next step is to Check the ECU connector, I pulled it and checked the connector and pins on the ECU for damage/corrosion/contamination, all looked good, there was a nice amount of dielectric grease in the connector. The next step was to check the communication line between the ECU and instrument panel at the ecu connector. This step is where I run into my first question, it has you check for voltage at the connector, I pulled the connector off of the ECU, turned the tractor on. I has you check for 12 volts across terminal 23 to 29, this tested out good. Next it has you test across terminal 30 and 31, you're supposed to get 5v, I got nothing. My question is are you supposed to perform this test when the connector is connected to the ECU via the back of the connector? I ask this because looking at the wiring diagram I couldn't figure out where the 5volts supply was except that the ECU produces it... to check this, I pulled the connector on the back of the HST Mode select/response control and found I had 0 volts on the terminals that should be connected to this same 5v circuit, however when I plugged the ECU back in and turned the tractor on, I had 5v across those terminals? Does the ECU generate the 5v for the sensor circuit? If so I believe the test I performed shows that the 5v circuit is live. After checking the voltage at the ECU connector it has you test the continuity between the ECU connector and connector b of the panel connector, this test was good. Those are all the tests it provides in the WSM to check the ECU. Am I to assume that if I've performed these tests the ECU needs to be replaced? Would a dealer be able to bench test the ECU to confirm it is bad? I did also use the panel to run the test mode and found there was no readings on T5-T16, all the sensors that the ECU manages, presumably because the ECU is not communicating because it has failed?... I tried to utilize mode "N" (Tractor Model Select Mode) and after selecting N it says "ECU SET" and when you press/hold the display mode switch it never goes to the "ECU-ADJ" that the book says it should... I just tried this because the book notes that if a new ECU is installed this needs to be done first, I didn't know if perhaps the previous owner had swapped it out and never set this and if not setting the ECU up could cause it to produce this error?

I'm hoping someone more experienced with troubleshooting these machines is able to give me some guidance, thank you in advance, and I look forward to being part of the community.
 

North Idaho Wolfman

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You will need to take the tractor to a Kubota dealer to have them read the unit with a diagmaster.
They will be able to tell if the ECU is bad.
 

North Idaho Wolfman

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Are they able to do this with just the ECU? It'll be easier for me to remove the ECU and take it than to load up the tractor again. Thank you!
I don't think so, because it need all the supporting components to test it.
 

whitetiger

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Are they able to do this with just the ECU? It'll be easier for me to remove the ECU and take it than to load up the tractor again. Thank you!
They will need the tractor as Diagmaster connects to the ECU through a diagnostic port in the main wiring harness.
 

Russell King

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But your dealer may be able to come to you for that service (if they are not to far away)
 

RDubbs

New member

Equipment
L5740HSTC-3
Sep 8, 2024
6
5
3
Seven Valleys PA
Thanks everyone, I'll call the local kubota dealer tomorrow and see what they can do for me, there's a Messicks about 18 miles away.
 

kubotafreak

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Did you try swapping the relays under the cab around yet?
 
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RDubbs

New member

Equipment
L5740HSTC-3
Sep 8, 2024
6
5
3
Seven Valleys PA
Did you try swapping the relays under the cab around yet?
On yhe lxx40 tractors there arent any relays under the cab, i think thats a different story on the lxx60 machines. On the lxx40 machines there are relays behind the intellipanel, I did swap the ones for the stop and glow but I didn't expect it to do anything, looking at the wiring diagram for the lxx40 tractors those circuits don't have anything to do with the ECU.
 
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kubotafreak

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GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Sep 20, 2018
1,049
394
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Arkansas, US
On yhe lxx40 tractors there arent any relays under the cab, i think thats a different story on the lxx60 machines. On the lxx40 machines there are relays behind the intellipanel, I did swap the ones for the stop and glow but I didn't expect it to do anything, looking at the wiring diagram for the lxx40 tractors those circuits don't have anything to do with the ECU.
Sorry just noticed this was the older poppet style injection. Sounds like if the main computer has 12v ref but no 5v signals then it may be suspect. The grounds to the ecu would be the other reason for a drop in circuit power. Have you checked circuits powered by the ecu. Just a guess would be circuits like the fuel cutoff, glow relay… powered circuits are what you’re looking for. Ive seen computers do odd things when bad sensors/actuators on the power circuits attached to the ecu. U can unplug the suspect ones to take them out of the circuit. I believe the ac system is separate on the tractors unlike cars. Otherwise id say disconnect it too.
 

RDubbs

New member

Equipment
L5740HSTC-3
Sep 8, 2024
6
5
3
Seven Valleys PA
So the latest on this, after the testing I tried above, I took it to the Kubota dealer Friday 9/13. They ended up confirming the ECU had failed and I had them order a new one. New ECU was received 9/19 and they installed it 9/20. These have to be "calibrated" to the machine, and they were able to perform the first step, telling it what machine it was in, but then when they went to go through the mode to calibrate the sensors it couldn't read the sensors. So it can start now, no error 20 code, but it won't move... they've been working with Kubota trying to troubleshoot it since. Unfortunately, I don't have the best information regarding what they've tried but I guess the concern is the new ECU wasn't programmed correctly from Kubota. I don't know, starting to worry how much this is going to cost me to get this thing up and running...
 

Moose7060

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I don't know, starting to worry how much this is going to cost me to get this thing up and running...
Don't worry, just remember your thoughts from your first post:

"and the tractor was priced that even if I can't fix it, I can part it out or possibly even purchase a similar model and just keep this one for parts".
 

kubotafreak

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Equipment
GRAND l6060, L3560, B6100, gr2100, tg 1860, g1800, g1900, g2160
Sep 20, 2018
1,049
394
83
Arkansas, US
So the latest on this, after the testing I tried above, I took it to the Kubota dealer Friday 9/13. They ended up confirming the ECU had failed and I had them order a new one. New ECU was received 9/19 and they installed it 9/20. These have to be "calibrated" to the machine, and they were able to perform the first step, telling it what machine it was in, but then when they went to go through the mode to calibrate the sensors it couldn't read the sensors. So it can start now, no error 20 code, but it won't move... they've been working with Kubota trying to troubleshoot it since. Unfortunately, I don't have the best information regarding what they've tried but I guess the concern is the new ECU wasn't programmed correctly from Kubota. I don't know, starting to worry how much this is going to cost me to get this thing up and running...
Get ready, I foresee them wanting to put a new harness on it.
 
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RDubbs

New member

Equipment
L5740HSTC-3
Sep 8, 2024
6
5
3
Seven Valleys PA
Finally following up on this. Not sure if it will help someone in the future. As I noted above, the dealer came to the same conclusion as I did, that the ECU was bad based on running the tests noted in the WSM (these tractors do not talk to the diagmaster). The received the new ECU and got stuck trying to calibrate the new ECU to the tractor. They thought perhaps the new ECU was faulty and submitted a ticket with Kubota, they told me this was "the longest case [they've] ever worked with Kubota" at one point. Apparently Kubota gave them many things to try and no success, at some point while my tractor was in another L5740 came in and they tested that machines ECU in my machine, after plugging it in all the sensors read out and seemed like all was good, again pointing to a faulty ECU (hindsite, apparently they didnt try to drive it... that'll make more sense in a moment). Kubota sent a tech out to help them with troubleshooting, not sure exactly how they figured this out but apparently the tech said he's seen this once before. During the calibration after telling the ECU what machine it is in, the next step is the calibrate the sensors, starting with the hydrostatic pedal, you cycle the pedal/solenoids, this is where the problem was, the solenoids on the servo regulator were shot and weren't firing. After replacing these solenoids they were able to finish the calibration and the machine works! Their speculation is that the machine likely quit working because of the bad ECU and then during the time that it sat the rust build up on those solenoids got bad enough that they failed and because they were bad at the time of setting up the ECU they got stuck in the calibration. If the machine had a working ECU during the time that the solenoids failed they would have been able to troubleshoot that more easily.

TLDR: The dealer along with Kubota figured it out, tractor works! My cost at the dealer was just for the replacement of the valves and the ECU (thankfully I didn't get charged for all the time spent on the troubleshooting and the tech flying in from Texas...) I've found a few small things that need to be replaced and been working on them (third function switch, return hose from third function block, oil change and all new filters, trans fluid looks good but will still likely change it in the spring, etc). All in all, I ended up with a nice machine that I'll slowly fix the little issues here and there on and I'm happy to be the owner of an Orange Tractor!
 
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North Idaho Wolfman

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Staff member
Lifetime Member

Equipment
L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
Jun 9, 2013
30,543
6,598
113
Sandpoint, ID
Finally following up on this. Not sure if it will help someone in the future. As I noted above, the dealer came to the same conclusion as I did, that the ECU was bad based on running the tests noted in the WSM (these tractors do not talk to the diagmaster). The received the new ECU and got stuck trying to calibrate the new ECU to the tractor. They thought perhaps the new ECU was faulty and submitted a ticket with Kubota, they told me this was "the longest case [they've] ever worked with Kubota" at one point. Apparently Kubota gave them many things to try and no success, at some point while my tractor was in another L5740 came in and they tested that machines ECU in my machine, after plugging it in all the sensors read out and seemed like all was good, again pointing to a faulty ECU (hindsite, apparently they didnt try to drive it... that'll make more sense in a moment). Kubota sent a tech out to help them with troubleshooting, not sure exactly how they figured this out but apparently the tech said he's seen this once before. During the calibration after telling the ECU what machine it is in, the next step is the calibrate the sensors, starting with the hydrostatic pedal, you cycle the pedal/solenoids, this is where the problem was, the solenoids on the servo regulator were shot and weren't firing. After replacing these solenoids they were able to finish the calibration and the machine works! Their speculation is that the machine likely quit working because of the bad ECU and then during the time that it sat the rust build up on those solenoids got bad enough that they failed and because they were bad at the time of setting up the ECU they got stuck in the calibration. If the machine had a working ECU during the time that the solenoids failed they would have been able to troubleshoot that more easily.

TLDR: The dealer along with Kubota figured it out, tractor works! My cost at the dealer was just for the replacement of the valves and the ECU (thankfully I didn't get charged for all the time spent on the troubleshooting and the tech flying in from Texas...) I've found a few small things that need to be replaced and been working on them (third function switch, return hose from third function block, oil change and all new filters, trans fluid looks good but will still likely change it in the spring, etc). All in all, I ended up with a nice machine that I'll slowly fix the little issues here and there on and I'm happy to be the owner of an Orange Tractor!
Thank you very much for the follow up.
Information is always helpful to someone at some point.