I have 1999 F350 Super Duty Crewcab diesel dually. Took it and got it scanned at Ford and it had P0715 and P0717 faults (turbine input speed sensor fault) stored but tech couldn't get them to reset . He said he couldn't command 4th gear and that he thought the torque converter was locking and unlocking continually at OD speeds. My speedometer works, I don't have oversized tires, fluid is clean and not burnt smelling and I have engine braking when going down hill. Any ideas what the problem is because this is the 2nd trans in less than 2 years.

 

Do you feel the TC locking and unlocking while in OD? It would be noticeable, it feel like a shift. Generally from take off its in first, then shifts to second and third, then TC lockup, then OD.

What trans do you have? Assuming ford reman since you were having it scanned at ford?
What style engine breaking do you have? Tuned break? Aftermarket?
What load are you pulling and at what speed?

 

I did when I took the truck up there this morning, at about 35- 38 mph, but when it got to between 43 45 mph it was like it would shift into od then immediately downshift. It's 4R100. And when I turn off OD going downhill at about 45=48 it starts engine breaking. The tranny in the truck now was replaced out of state and no it's not a Ford but thought Ford would be best place to get scan. I don't know what kind of engine breaking I have. But I do know my truck has a banks system on it.

 

A bad torque converter will not set the P0715 and P0717 codes. Neither will a bad transmission.

It is not surprising that the tech couldn't reset the codes. That means that there really is something wrong and it needs to be fixed. I recommend taking it from this dealer that apparently has NO CLUE and take it to a place that knows how to do diagnostics. Some dealers can, and many independent shops can. Not a transmission shop, a general repair shop.

Either you have a bad speed sensor or a damaged wire to the speed sensor. You need someone that knows how to find that out.

 

Thanks, that's kinda what I was thinking. The other didn't make sense. Again thanks!