2011 FORD RANGER XL 2.3 2WD AUTOMATIC


So I had problem with my truck getting stuck in low gears with overdrive flashing (2nd gear I believe was most frequent, it would not shift up to 3rd but in the earlier stages if I let off the gas it would shift up to third), I could not get my truck into reverse most of the time but on occasion it would fall into reverse and kind of bog out but atleast I could back up a bit, lastly a heard grinding noise coming from what appeared to be my transmission, so I went ahead and grabbed a junker transmission and swapped it out.

On installing the new transmission, I found that I ended up having very similar issues after firing it up. Slipping gear trouble and a hard time switching from 2nd to 3rd gear... And of course no reverse. Overdrive again flashing. Strange thing is, if i shut the truck off and start it back up it goes back to normal for a few minutes until it ends up going haywire again. But hey! Atleast the grinding noise isn't there (for now atleast)

Part of me wants to believe this is something electrical, but I'm also dont trust junkyard parts.

On the new junkyard tranny I pulled 3 codes:
P0733 (gear 3 incorrect ratio)
P0734 (gear 4 incorrect ratio)
P0735 (gear 5 incorrect ratio)

I've heard everything from replace the servos to solenoid pack...

I'm not a professional mechanic, just an HVAC guy who wants to learn a little bit.

Where and what should I start with?
Any help would be much appreciated!

 

Have a look here at the transmission codes the computer can use: https://www.therangerstation.com/tec...II_codes.shtml

Automatic transmission codes are in the P0700-P0799 range

It would set an electrical code, like "P0753 Shift Solenoid A Electrical", if thats what it was, the codes a computer does NOT use are as important as the ones it does use, thats why looking at a full list is helpful, versus googling a single code number
Just FYI

Yes a used automatic is a roll of the dice, at the best of times
Were there any codes from the old transmission?

All automatics run on Fluid Pressure, thats what engages Forward and Reverse, and what shifts the gears
You need 120psi pressure to engage Forward, and 160psi to engage Reverse, this is why Reverse failing, or slow, to engage is often the 1st sign of a transmission issue

Fluid pressure is generated by the Front Pump(only pump, lol) it is inside the front of the transmission connected directly to the torque converters outside housing, so pump spins at engine RPMs, raising RPMs increases pump speed and pressure
The fluid pressure is sent to the Valve Body and it routes fluid pressure thru passages that are controlled by valves to engage and disengage clutches and bands(brakes)

In the "old days" valves were operated by springs and ball valves, with cables and vacuum thrown in, lol

Now-a-days valves are operated by solenoids and springs, the solenoid moves its valve and spring pushes it back when solenoid is off

So thats the basics

If the codes were similar between the two transmissions then I would think the computer was the problem, it has a software, like any computer, that it uses for operating the transmission, and like any software it can be corrupted, its rare for sure, but not unheard of.

The fact it is generating codes should mean the software is OK, and the fact the engine is running OK should mean the computers hardware is OK

So its a tough call, on where to go next, if the used transmission had a warranty period then I would use it to get another one