ERROR CODE 78 TN90F

[new holland 11]

I have a New Holland TN90F tractor. The Power Shuttle does not work.

On the dash there is an error code flashing looks like a book with power shuttle symbol (the power shuttle alarm indicator)which flashes yellow approx 4 or 5 times quickly, Pause, followed by 7 normal yellow flashes, Pause, followed by 8 normal yellow flashes. (Error Code 78 I believe meaning that the Internal Electronic Control Module voltage is/was below 8Volts.)

Also I have not started for a while and battery was completely drained to zero, I recharged slowly with 2 amp charger overnight and now starts right up like it is supposed to, but power shuttle does not work. (It worked fine when last parked, 2 months ago)

Any ideas on how to correct this?

 

[HenryFordPower]

I have a New Holland TN90F tractor. The Power Shuttle does not work.

On the dash there is an error code flashing looks like a book with power shuttle symbol (the power shuttle alarm indicator)which flashes yellow approx 4 or 5 times quickly, Pause, followed by 7 normal yellow flashes, Pause, followed by 8 normal yellow flashes. (Error Code 78 I believe meaning that the Internal Electronic Control Module voltage is/was below 8Volts.)

Also I have not started for a while and battery was completely drained to zero, I recharged slowly with 2 amp charger overnight and now starts right up like it is supposed to, but power shuttle does not work. (It worked fine when last parked, 2 months ago)

Any ideas on how to correct this?

Does your tractor have a 12x12 or 24x24 transmission?

 

[HenryFordPower]

Does your tractor have a 12x12 or 24x24 transmission?

There is supposedly no wire to pin #35 on 24x24 or 12x12 transmissions which is where the error 78 is being derived from. It must be shorting out. I am working on determining where pin #35 at connector 2 is at. It must be grounding out at that point in the wiring harness. I will post a diagram when I find it.

 

[RickB]

Does your tractor have a 12x12 or 24x24 transmission?

A TN90F with Power Shuttle built in North American configuration will have a 32x16 transmission.
Fault code 78 nearly always results from the failure of the ECU.
If the Power Shuttle ECU on a TN90F is still the original, I'd be all but certain that it will take a new ECU to get the OP up and running.
Pin 35 on ECU connector C-2 is not used; the circuit fault originates from within the ECU. I suppose it is possible to check pin 35 for a short to ground or 5V, but I have always R&R'd the ECU based on fault code 78.

 

[HenryFordPower]

A TN90F with Power Shuttle built in North American configuration will have a 32x16 transmission.
Fault code 78 nearly always results from the failure of the ECU.
If the Power Shuttle ECU on a TN90F is still the original, I'd be all but certain that it will take a new ECU to get the OP up and running.
Pin 35 on ECU connector C-2 is not used; the circuit fault originates from within the ECU. I suppose it is possible to check pin 35 for a short to ground or 5V, but I have always R&R'd the ECU based on fault code 78.

I agree that the fault is almost certainly originating in the ECU, however it is worth a try to see if there is a short at the unused Pin #35. Can connector CN-2 be replaced without the complete harness? Maybe the short originated there?

 

[RickB]

I agree that the fault is almost certainly originating in the ECU, however it is worth a try to see if there is a short at the unused Pin #35. Can connector CN-2 be replaced without the complete harness? Maybe the short originated there?

If there is a short at pin 35 of connector C-2, the short is within the ECU, not the harness. Pin 35 of C-2 is in the connector half that is an integral part of the ECU. The chassis harness connector half of C-2 has no wire in position 35 (as you stated yourself) and IIRC no metallic socket for a conductor to connect to, so therefore it is impossible for the short circuit to orignate in the harness unless there is a piece of tramp wire floating in the harness connector which is unlikely to manifest itself after 10 or more years. A visual inspection of the back of the connector can't hurt but the person doing the inspection might as well have a new ECU in his other hand. Not many folks are going to chase a short circuit within that ECU.

I've been wrenching on these TN/F tractors from their beginning up until a couple years ago when I moved to the parts dept.
I don't know everything about them, but I have figured out a couple things here & there.

 

[HenryFordPower]

I certainly appreciate your knowledge, please dont take my posts in the wrong direction at all. I am trying to learn as well as the OP and adding some possibilities along the way. Thanks for the info, it is MUCH appreciated. Discerning ASSIST as you probably well know can often be a task in and of itself.

 

[RickB]

I certainly appreciate your knowledge, please dont take my posts in the wrong direction at all. I am trying to learn as well as the OP and adding some possibilities along the way. Thanks for the info, it is MUCH appreciated. Discerning ASSIST as you probably well know can often be a task in and of itself.

No offense intended or taken.

 

[HenryFordPower]

No offense intended or taken.

None here either, keep on keeping us informed.

 

[new holland 11]

Thanks All...Sorry I didn't get back sooner. The next day I went out to the barn and started her up and no issues or errors and everything worked fine. Maybe with the battery being dead for a while did something? I charged it with the battery cables connected, maybe that threw something off? Should I be disconnecting the battery cables before charging? From now on I'm just going to start it every two or three weeks and let it run a while. I really love this tractor, but sometimes I wish it was more like my Massey 175, I don't have to baby that one...leave it out in the rain, who cares...she always starts and goes.