I certainly don’t know everything, so I ran this scenario by a few of my coworkers and they ALL immediately asked if you have already reinstalled the original pan and if it has Toyota WS.
It seems like you are holding fast to shotgunning an ECM at this problem. I’m not sold on the idea, but if...
The ECM bases its output to the TCM on many different things. I’m not certain you CAN force an output. The signal the ECM outputs is a pulsed waveform.
But what you could do is active test the SLT solenoid via GTS+ (“Techstream”) and see what happens with that.
The solenoid codes aren’t based...
The SLT signal from the ECM/PCM is a pulse modulated signal, so you’d need a PicoScope/oscilloscope to check that properly.
Replace the pan with OEM and use Toyota WS fluid and go from there.
That advice is usually regarding a flush if there’s not a history of transmission services.
Otherwise, yes definitely do a drain and fill. I would really recommend doing 2-3 drain and fills, spaced a few hundred miles apart.
Make sure to set the fluid level properly.
I’m not CERTAIN, but I remember the last time I priced one it was a little less than $4k. Under 100k I don’t think a torque converter is necessary if you’re maybe on a bit of a budget, but at your mileage it may be worth it.
I’m a fan of these wheels.
For anyone with a 2015 and older LC, you can use the 2016+ LC wheels on the 2015 and older models by replacing the front hub grease caps with the lower profile 2016+ LC grease caps. Otherwise, the center caps will not seat all the way into the wheel.