My 2003 5.4L F-150 with a 4R70W transmission suddenly started stumbling and wouldn't go above 30MPH with the OD light on gear selector flashing.
I had recently changed the transmission fluid and filter about a week ago. Didn't note any metal in the pan. Used Mercon V and made sure the fluid level is correct.Put about 40 miles on it and it drove fine.

Changed the front and rear differential fluid and the 4WD transfer case fluid with Mercon LV yesterday and a few miles later, the problems started happening. I doubt it has anything to do with changing the differential fluid.

Pulled the codes and I get a P0750 (Shift Solenoid A), P1747 (Pressure Control Solenoid A Short Circuit), P0755 (Shift Solenoid B), and P0743 (Torque Converter Clutch Solenoid Circuit Electrical).

Googled and YouTubed this and it saw some videos that indicated a bad wiring harness. Put the truck on a lift and inspected what I could of the wiring, including pulling the fender wells. I could not find any damaged wiring.

I have a hard time believing that this is a catastrophic transmission failure as the transmission has been serviced with fluid and filter every 40-50K miles and the truck has always run great... A hard failure (lots of metal in the tranny) could cause P1747 according to one YouTube video. Really don't want to pull the pan as everything looked great when I changed it last week... No metal and the old fluid was nice and red.

 

I hope you used 75W90 or 80W90 in the front diff and 75W140 full synthetic in the rear diff, not Mercon LV.

 

Yes, used 75W140 with limited slip additive in the rear and 75W90 in the front diff.
Mercon LV is now Ford recommended for the transfer case...

 

You may have a broken wire in the harness or the internal transmission harness may have broken. You're going to have to check the harnesses to determine what the problem is.

Pay attention if it happens all the time or just when it's warm or cold. That info might be useful later if you get stuck trying to diagnose the issue.

Unplug the connector at the back, passenger side of the transmission. With the key in the run position (engine off), check pin 4 at the harness plug for 12V. If you have 12V, start checking continuity on the transmission connector to test for a broken internal harness.

Check between these pins on the transmission connector:
*Pin 4 and Pin 3 (TCC) 10-16 ohms
*Pin 4 and Pin 6 (EPC) 2.48-5.66 ohms
*Pin 4 and Pin 7 (SSA) 20-30 ohms
*Pin 4 and Pin 8 (SSB) 20-30 ohms
If the internal harness shows no or very little continuity , then you'll have to drop the pan and inspect/test the components individually to find the issue.

If the internal harness and solenoids check out alright, then you're going to have to check for continuity between the wires from the PCM plug and the corresponding pins on the transmission plug. You'll also have to check between pin 3 of plug C110 and pin 4 on the transmission harness plug. Plug C110 is a grey, slightly rectangular shaped plug with about 37 wires in it. It's located to the right of the PCM.

Transmission plug (harness side).

 

Looking at the wiring and not finding a problem does not mean the harness is good. How does it test electrically? Without knowing that you can't tell if the harness is good or bad.

 

That's true... I checked the easy and obvious stuff first...
Also checked every fuse in both fuse boxes and all checked good with a continuity tester.

So, off to check the wiring harness.
Fortunately for me, I just got done building a shop with a lift
Unfortunately, the new truck money went to the shop

 

Verified 12V on pin 4...

Due to the way the connector on the transmission is oriented, I don’t see a way to check it without a section of wiring harness or pulling out the transmission...

I need to find a wiring diagram for the truck... maybe I can check it at the other end of the harness...

 

Now the truck won't even run properly. The engine is running rich and stumbling at idle.
Tried disconnecting the battery and waiting a few minutes to reset the engine computer... didn't work

 

I thought my 08 had room there when I put the trans. in it. Maybe the heat shields were off at the time. I don't remember. Sucks getting old.

 

C110 plug pin ----- C110 plug pin --------Component
--------3----------------------36 ---------------TCC solenoid
--------3----------------------37 ---------------EPC solenoid
--------3----------------------33 --------------------SSA
--------3----------------------35 --------------------SSB

If everything checks out alright, you can test the little section of wires between the PCM plug and other half of the C110 plug.

PCM plug pin ----- C110 plug pin
--------54--------------------36
--------81--------------------37
---------6-------------------- 33
--------11--------------------35

 

Thanks a LOT for the diagrams.
Pulled the battery and tray and pulled the plug to the PCM.
Rigged up a test lead and continuity tested from the PCM connector to the transmission connector... everything checked out fine...no shorts.
I couldn't check the resistance because I couldn't figure out how to get to pin 4 on the transmission harness from under the hood.

Anyhow, I think this points to a short or something seriously wrong inside the transmission.
I notice that I can purchase all of the solenoids, internal harness, filter and gasket from Global Transmission Parts for a bit over $100.
From the YouTube videos I have looked at, it looks fairly simple to replace everything.

Question... Can I disconnect the transmission harness and drive the truck at low speed so that I can move it around my lot?

 

I think I'll just put it up on the lift tomorrow and pull the pan…
I'll pull the internal harness, inspect it and check the continuity, and check the resistance of the solenoids from inside the transmission.

 

Pin 3 in the C110 plug supplies pin 4 on the transmission plug. I guess I should have been more specific earlier.

I posted this earlier so you could test the path and solenoids via the C110 plug.

C110 plug pin ----- C110 plug pin --------Component
--------3----------------------36 ---------------TCC solenoid
--------3----------------------37 ---------------EPC solenoid
--------3----------------------33 --------------------SSA
--------3----------------------35 --------------------SSB

 

From what I can tell, the external harness appears to be just fine.
Reconnected the PCM wiring harness, re-installed the battery and left the transmission disconnected.
The engine ran fine and I drove around for about 2 miles. Seemed like the transmission only shifted to 2nd or third gear ( I couldn't really tell).
Other than that, it seemed to drive OK.

Put the truck on the lift and pulled the pan... Everything looked to be in order...nothing catastrophic.
Pulled the wiring harness (broke the release clips, so I'll have to order a new one...oh well).
Checked the resistance on the solenoids...within the proper range.
Checked for a short in the wiring harness (molded plastic)..No shorts, continuity checked good.

I did note that the external harness connector was a tad oily...and it looks as if a bit of fluid may have somehow traveled into the external connector.
Would this cause the PCM to go nuts?
I had initially overfilled by a bit less than a quart and ended up using a suction gun and tube to pull out some excess fluid from the dipstick.

Wondering if I should change out the solenoids while I am at it or just leave things alone.
I'll hit the external harness connectors with some contact cleaner before I re-install it.

 

Did you find the issue yet?

If the connector in the trans is leaking, that could be the cause of the problem (especially if you've ruled everything else out). They have been known to cause issues when leaking. You'll have to remove the valve body to change it out, so make sure you pick up a new gasket too.