Hi everybody! I am new to this forum and looking for some answers about my truck's tranny. I have a 1999 F-150 4x4 Off-road. I have a 204,000 miles on my truck. It has a 5.4L, 4R70W Transmission and 3.73 gears.

About 2 weeks ago, I saw that my OD off light was flashing. So I broke out my scan tool and I had a P0781 1/2 Shift code. Up to this point, the tranny has been bullet proof. I've had no issues at all. I did some investigating and I read that the shift solenoid goes bad. So I replaced the shift solenoid pack, the TCC solenoid and the EPC solenoid. Along with the filter. After replacing those, the next day, bam! Same issue. So I did more digging and noticed that the 1/2 accumulator and springs go bad. So this weekend I replaced the accumulator, lower spring, and upper spring. I just went for a long drive. Everything drove fine. The shifts were smooth through all the gears. Then about 20 minutes in, the damn OD light was flashing at me!!! Then the first into second gears were rough and they were rough coming back down. Just like they have been from the start. I hooked up my scan tool and sure enough was P0781 staring me in the face! There are no other codes.

It seems like it only happens after the light flashes on and off. I just checked all my fuses and the battery connections. I pulled the negative off to see if the maybe the computer needed a dump.

Could it be the wire harness that runs across the valve body to all the solenoids? That is the only electrical component outside the valve body I haven't replaced. I read to replace my radiator that maybe its clogged, I did that last year or so.

Please help!! I want to figure this out before having to bring it to a shop and have them rake me over the coals.

Thank you for all your help! I look forward to talking to you guys soon!

 

If it were an electrical issue it would set a code for the electrical circuit that had a problem. I suspect you have a worn intermediate clutch.

 

Thanks for getting back to me, Mark. That doesn't sound too good. I haven't torn apart a tranny in about 6 years. If I remember right, I gonna have to drop my tranny to get to that clutch right? At that point I should consider doing a rebuild?

I would get a code for that harness, not the shift code? Is there anything else that it could be without dropping the tranny and doing a rebuild?

 

To get to any of the clutches the trans has to come out. If you have to replace one clutch it makes sense to replace them all, which is a rebuild.

There are codes that indicate electrical problems. These are the most reliable codes that can set. If there is no electrical fault code then it is about 99.999999% sure that there is no electrical problem. That's been my experience, others may care to differ.

The only other possibility is a sticky 1-2 shift valve in the valve body. In my experience this is less likely than a clutch problem, but certainly not impossible.

 

I'm not trying to insult your knowledge, Mark. But I do have a code for my transmission. I have a P0781 1/2 Shift code still as of today. Could it be that plastic electrical harness that runs to all the solenoids?
If I manually shift the truck from 1 to 2 or 2 to 1 it seemed like it shifted OK. But when I had it drive I can feel the rough shifts. Wouldn't I feel rough shifts by manual shifting if I had a worn intermediate clutch?

 

You DO NOT have a code for an electrical problem, so I don't know why you think it is an electrical problem. Change whatever wiring you think is the problem and let us know how that works.

 

Let's not get out of control, sir. I'm am just trying to see if there are any other possible things that this issue I have can be before I spend hundreds on a rebuild kit or thousands on a transmission. Not only that but the time I will spend under my truck away from my family. If this problem is the intermediate clutch, then that is what it is. I will look to pursue that path for fixing that problem as you suggested. I did not mean to upset you any way or to insult you, but it seem I some how have.

Thank you for your time answering my questions and I look forward to maybe discussing things with you in the future.

 

Mark was a transmission engineer and knows these things inside out, but note this regarding P0781:

P0781 FORD - 1-2 Shift Error

Possible causes

- Low transmission fluid level
- Dirty transmission fluid
- Faulty shifting solenoid valve
- Shifting solenoid valve harness is open or shorted
- Shifting solenoid valve circuit poor electrical connection

When is the code detected?

The P0781 code is detected when the engine RPM did not drop during the 1-2 upshift

Symptoms

- Engine Light ON (or Service Engine Soon Warning Light)
- Transmission may not shift to the next gear.

P0781 FORD Description

This P0781 code indicates that the 1-2 shift valve in the valve body is locked in the direction of the spring compression. The Transmission Control Module (TCM) controls the gearshifts by turning the shift solenoid valves "ON/OFF" and switching oil pressure to the valves in the valve body. The TCM calculates the "actual" transmission gear by comparing the signals from the input speed sensor and the output speed sensor.

Read more: http://engine-codes.com/p0781_ford.html#ixzz2VuwZKiPr

I am NOT a transmission tech, but I'd probably look at that harness before dropping the tranny.