2003 Expedition 5.4L 4x4 FX4, 175K miles, original motor and trans. Suddenly threw several codes and went into limp mode (about 40 mph max and gutless), flashing "O/D" light and steady "Check Engine" light. Had codes read at a local shop since I was in town at the time and they said it was a "bad shift solenoid". I went ahead and replaced all 3 solenoids myself in the 4R70W transmission, thinking that would solve the problem on the cheap, unfortunately it did not. Tried resetting codes and they immediately return, here are the codes...

P1747 - pressure control solenoid A short circuit
P0750 - shift solenoid A
P0755 - shift solenoid B
P0743 - torque converter clutch circuit electrical
P0141 - 02 sensor heater circuit bank 1 sensor 2
P0161 - 02 sensor heater circuit bank 2 sensor 2

Obviously not just a "bad shift solenoid" code like the shop told me, and not all trans related codes. Which makes me wonder if this is either a broken/pinched wiring harness somewhere, a blown fuse or relay, or a bad PCM. The one thing I did not replace, but could have as I see it in some of the 4R70W kits, is the black plastic wiring harness that connects the solenoids. Although, I can't imagine that both 02 sensors would fail at the exact same time.

Maybe a huge coincidence but this limp mode all started as I left the drive through oil change place, which I immediately returned to. We put it back on the rack and I went underneath with the tech to look around, they really did nothing other than drain/fill the engine oil, trans oil level was good, and they are established competent guys that I trust. Couldn't see a scenario where they may have damaged any wiring.

Any help on where to start looking is GREATLY appreciated. I've had the vehicle since it was new and while it is a great "extra" vehicle that we keep at our vacation home, given the mileage and other small things it needs, like control arms (again), tires, etc, if I cannot figure out how to fix this myself for a few hundred bucks it's probably going to the crusher. Not willing to pay shop rates to diagnose this one, but currently stumped.

Thank you!
Kris

 

This could all end up being something simple, but WILL REQUIRE some serious checking .
If you are determined to send it to the crusher, maybe you could get more selling it as is and the purchaser will invest in a good diagnosis and have a usable vehicle.

The clue here is the "shorted circuit" and a good tech will check wiring and connections for touching an unintended ground.

Suggest having a "cold one" or a couple cups of coffee and think this through.
Are you game ?

What if you took a good look at the fuse panel, corrosion anywhere ?

 

I've got some time tomorrow morning, will start with the fuse panel(s), then start chasing wires around looking for anything obvious. I was really hoping somebody would have seen something similar and know where to start looking, don't have a good method (at this house) to get the thing up very high in the air.

 

It does not have to be under the vehicle. Maybe it was something they moved to add the oil. May not be more than a coincidence to happen after an oil change.

Any worthwhile diagnosis starts with a good and thorough visual inspection and you know what is under that hood better than most folks. Many times we move a harness that was too close to a sharp bracket and the problem went away, maybe a wire or wires could be too close to a source of exhaust heat. Frustration can get the better part of our patience and there really aren't that many "silver bullets" that solve problems like this easily.

 

Well, the Expo got a stay of execution today. I started chasing wires around and it did not take me long to find what appears to be that "silver bullet". On one of the main wire looms coming off the PCM there was a spot where the protective wrap was completely gone, probably got brittle and flaked off. One of the wires, purple wire with white stripe, was chaffing against the metal AC condenser piping and had worn through (see pics). I repaired the wire and added some new loom to protect it. Started the vehicle, still in limp mode with warning lights, same codes. I went to the book and found the fuse I was looking for without having to pull each one and check (see pic), fuse #32 handles transmission solenoids and catalyst sensors, bingo. Pulled #32, blown. Replaced 15A fuse, upon startup all warning lights off, codes are gone. Vehicle runs great, or at least as good as it did before.

Thanks Hanky for the insight! Hopefully this post can help someone else in the future.