Mechanics and DIY fixers: Diagnoses on Automatic Car Error Code?

Error code P0750 on Ford Focus 2007. Already replaced Solenoid A as well as a Transmission Fluid Flush a month ago. Saw exposed wire for Sol-A and cut and reattached the wires with solder, no protection over soldered wires. I saw today that the Transmission Fluid is dirty, despite a flush a month ago. Does the Error Code deal with something else other than the Solenoid? Websites aren t helping me

Quick Google search

So my friend has a 2003 Ford Focus ZX3.
She called me to ask me to have her transmission replaced.
Not knowing much about cars, I told her I'd check it out before she spent almost $2800 in a new one (including labor) or $1750 for a used one (with labor).

Upon driving it, I realized that 1st, 2nd, and 3rd (Drive) worked properly.
It was 4th (overdrive) that had the problem.
Upon shifting into OD, the car would free rev and not pull/move anymore.
By simply clicking the OD button to OFF, the car dropped back to 3rd (Drive) and pulled fine.

I pulled the check engine light (CEL) code and got P0750.
This calls out a failure in Solenoid A.
The part number from Ford on this is XS4Z-7H148-AA.
Cost is around $50.

To change this solenoid is relatively easy, it's just messy.
In one of Ford's worst ideas, there's no drain plug in the transmission.

So you have to loosen/remove 19 bolts from the pan.
Leave 1 bolt (the 20th for those counting) in and slightly loose.
You'll need to break the seal (silicone) between the pan and trans loose. I used a rubber hammer and a flat blade screwdriver

Drain all fluid out (about 3 quarts) and then remove the pan.

Locate Solenoid A. It's the only one with a WHITE wire going to it.
Unplug the connector and remove the bolt holding the solenoid in.
Simply pull the solenoid out.
Install the new solenoid in the reverse manner above.

You'll have to clean all the old silicone from the transmission mounting surface and the pan. A wire brush and some carb cleaner work great.
Apply a thin layer of high-temp silicone to the pan and the reassemble to the transmission.
Let the silicone set in place overnight (or up to 24 hours per directions on the tube).
Refill with Mercon V fluid (about 3 quarts).

Clear the CEL code in the computer and go for a test drive.
Voila! Problem solved.

Total materials - < $75

That transmission was trouble from the start. Ford knows it and has no remedy. It's a bad design. Get a rebuilt and have the computer reflashed to shift it right. That car should have been recalled and Lord knows Ford has swapped plenty of transmission under warranty for the Focus.

See here:
https://www.autocodes.com/p0750_ford.html

The main reason for the code is based on the management system measuring the solenoid current when it operates.

It implies you still have a wiring fault, or the bare wire you mentioned shorted to metalwork and caused a high enough overload to damage the control module (or blow a fuse somewhere?).

The picture in that article appears to show a ground wire attached near the base of that solenoid - is that OK?
A bad current return path can cause similar problems to a bad feed circuit…

It does also say that dirty fluid can be a cause, so possibly there's a pressure switch somewhere monitoring the hydraulic circuit the solenoid controls & a clogged-up valve duct can mess up the pressures.

Another flush may be needed?