TN75SA power shuttle problem?

[Dayscreekrancher]

Hi all,
I'm having trouble with my 2005 NH TN75SA tractor. While I was using the tractor, it stopped going into gear. After futzing with it for a while I was able to get it to move a short distance to a parking spot. I haven't been able to move it since. It is a 16x16 with power shuttle, cab, 4wd and supersteer. There are no dash lights lighting up (other than normal battery light before start, parking brake and 4WD), no flashing error codes and no indication that anything is wrong other than no forward or reverse motion.
Fluid levels are good and the engine runs well. I also searched for blown fuses and eventually found a 10amp fuse that blows, but I cannot find a fuse diagram for this tractor. The operators manual that came with the tractor has a completely different layout than the actual fuse box. Any ideas or troubleshooting starting points?

 

[1bush2hog]

Check under the seat area to make sure wires are all plugged in. I had a connector that was unplugged, resulting in similar issue

 

[charleyfarmall]

Does it work if you replace the fuse or does the fuse blow immediately? Look for chafed wires that could be shorting out. If that's not it, you may have a bad solenoid in the transmission and it might be a dealer fix. Take a flashlight and looks under the dash too. The black panels should come off with a screwdriver. This is the downside of fancy transmissions - how are we going to deal with them 20+ years down the road when the electronic boards are no longer available...

 

[Dayscreekrancher]

I found the short. It was in the seat. I've bypassed the seat circuit. The circuit breaker now does not blow anymore.

BUT.... No improvement on the transmission. Do you know a way to check the selenoids in the transmission?

 

[charleyfarmall]

I don't know how but that's because my TN75 has been very reliable so far. Actually now it sounds like you have a loose connection - maybe a plug came undone under the tractor.

 

[Dayscreekrancher]

Well, I finally solved the problem. After much work at the dealer (local dealer had trouble so I borrowed his manuals and worked through the problems) we discovered that the power shuttle ECM was totally dead. This is the control module for the transmission. No error codes, no outputs, no work. A total of 300 hours on the tractor and the computer totally failed. A new computer and I'm up and running, but......

I very worried about the future!

 

[mytreefarm]

Hello, I'm having similar symptoms with my 2003 TN65 with 16x16 power
shuttle. 140 hours just stopped moving. Engine starts, runs fine I saw no error codes. How did you determine the ECM was bad? I have no blown fuses. I have unplugged / replugged most of the switches/sensors looking for a bad connection/wire. So far all connections look/measure good. I have the service manuals. No flow chart to help with logic flow. Just circuits.
The tractor is clean, stored inside, have found no signs of mice.
I'm suspect of the clutch sensor or ECM. The clutch pedal felt soft(response lagged) just prior to the fail.
Dealer is a long drive/tow. I'm thinking I may be better off to swap some parts if I can formulate an educated guess.
In a nut shell, how do I narrow the area of fail? Can I jumper some of the
switches/sensors to help with debug?
Thx

 

[Dayscreekrancher]

The short (and unfortunate) answer is if you are having the same problem that I did, then it is very difficult to tell for sure that the ECM has given up. I worked side by side with a technician for several hous before we finally guessed that the ECM was the culprit. That said, here are a few pointers that may be useful to you.

1) New Holland has a scanner that can be plugged into a port under the dash to read error codes and reset the ECM, etc. This is an essential device if you replace the ECM as you will need to do several calibration steps before the new ECM will function properly with the tractor.

2) To make the scanner useful, you will need the manual for the scaner (I assume it comes with the scanner), but it may be specific to each tractor model.

3) You will also need the service manuals. These are very useful once you get an error code to troubleshoot. Also, with the schematics you can check that the ECM is properly connected to everything in the tractor.


The symptoms you describe are very much like the symptoms I experienced with my tractor. My tractor did in fact move two more times after the initial failure. Apparently when the ECM went, it didn't go 100% immediately. All engine function appeared normal, PTO turned, I could feel a very slight shudder as I put the gear levers in and out of gear.

Since the ECM controls the transmission, it is very capable of disabling the transmission if it detects a problem. When it does this, it is suppossed to give an error code. If it is not giving an error code, then the ECM is probably not functioning. It could be the ECM itself or the wiring going to the ECM or I supose even the wiring going to the dashboard.

I had a few small ancillary problems that muddied the problem, but as I cleared them up I saw no improvement whatsoever in the functioning of the tractor.

My trouble shooting steps were:
1) checked all gear linkages to make sure there were no bent, broken, disconnected linkages.
2) checked all fuses
3) checked brake fluid (yes, there is a sensor on the brake fluid resevoir). You can fool this sensor teporarily by removing the cap and turning it upside down.
4) checked all fluid levels (only transmission/rear end should have any bearing on the issue).
5) visually checked all wiring, connectors, etc.
6) looked multiple times for error codes blinking on dashboard - found none, confimed that dash lights function (all should turn on when you first turn the key)

- trailered tractor to dealership which gave me access to manuals and scanner.

6) read error codes off of scanner, spent 2 hours trobleshooting 2 error codes before determining that we had the wrong connector plugged into the scanner
7) plugged scanner into proper connector and got no response from the ECM.
8) physically checked all connectors to the ECM (there where 2 large connectors on my ECM) we took them off, cleaned them and reconnected them.
9) Using schematics in service manual, looked for missing supply voltages to the ECM. The technician working with me said he had seen a case where the ECM was not getting power to one of the power inputs and this caused a similar problem.

10) plugged a new ECM into tractor (technician was surprised that the dealer had one in stock) This fixed the problem.

11) calibrated ECM

So, you might be asking, "Why not just plug a new ECM in and see if it works?"

You can do this, but it is expensive and you still need to calibrate the ECM if it does work. The ECM cost ~$750.00 and I was told it would be a non-returnable special order.


GOOD LUCK! Please post back to let me know how it is going.

-Don

 

[mytreefarm]

Excellent POST. Thank you.
Currently I'm going thru the schematics again to identify circuits I can bypass, as you suggest, such as the brake fluid.

Now that you mention it I don't recall seeing the dash indicators on when the key is in the ON position. The parking brake indicator is on and one adjacent indicator, no others.
I'll keep poking but a 3 hour trailer ride to the dealer may be in my future.
I like the Power Shuttle, however, having the tractor down with only 140 hours is very disappointing. Lesson learned - always stay mechanical, avoid electronic control.
I'll POST developments.

 

[ironpen]

I have a 2002 or 03 TN75S and I have developed a similar problem. The only way it will move is to put it in gear and engage the power shuttle with the clutch depressed and then release the clutch. If I put it in gear and move the power shuttle to engage, the yellow light blinks on the dash and nothing happens. If I push the clutch in and let it back out, everything then engages and I move away normally. The beeper that indicates the parking brake is not on that makes that god awful racket (until you put the parking brake on when you shut the tractor off) makes the same racket when I put it in gear as I am taking off and then stops after about 12 beeps. For a while that same beeper would just come on periodically while using the tractor, but the dealer replaced the switch under the seat and that stopped.....except when I put in gear and first drive away. I guess I should be happy I figured out what to do to make things operate normally except the power shuttle should not require that I depress the clutch all the way, put the power shuttle lever in forward or reverse and THEN let the clutch out to make it engage. It will go from forward to reverse without depressing the clutch just like it's supposed to. My dealer has tried but has no answers at this time. Anybody with a similar episode. Not exactly like described above, but it smells similar to me. I have about 1200 hours on the tractor. Very pleased with it overall, but I would like to resolve this if I can so I won't get stranded someday. Thanks.