2004 Buick Rainier same problem. Power drivers seat won't move

Question edited to remove the abbreviated 'transmission' word.
Question moved to model category.

Call out a Mobile Auto-Electrician. They can use a pro grade scan tool computer to diagnose all the transmission electronics, sensors, solenoids, modules and check for codes. The problem is electronics, not the transmission itself.

https://www.google.com/search?q=auto+electrician+near+me

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more than likely it is the power seat switch itself try pushing on theforward button really hard onc and if it now moves get a new switch

So here is a diagram of the seat circuitry for your car. Since every other function works except the forward/backward slide function, that leaves basically the forward/backward slide motor, the seat switch, and/or the wiring. If you can verify that the wiring under the seat is in good condition without obstructions, chaffed wires, and/or wires pulled too tight, then it's safe to say it's down to just the motor and/or the switch. Sometimes if the passengers front seat has the same switch, you can plug it in to the drivers' side connector and see what works and what doesn't. If the seat works fine with the other switch, then that's all it needs, if not then it will need a motor. If the other seat doesn't have a switch then you can find them at wrecking yards, or just supply power and ground to the motor in question to see if it works. If it does, then you know you kneed a switch and if not then a motor.
I hope this info helps!~subyguru~

check the fuse; the fuse box it's located under the dash on the left of the foot rest (drivers side)

find seat plug make sure its getting power check ground check all fuses inside and outside of vehicle

it sound like you need to replace seat control switch

woman with a hammer fixed 2004 Rainer! Had same problem. just tapped rear runners with hammer and it broke loose. Works fine now!!!
Hope it works for you.

I have had the same problem. It occurs when you take the key out of the ignition to fast. Sounds stupid but if you turn the engine off and slow down the extraction of the key the seat will move as it should. I was turning off and taking the key out fast and the seat would not retract. Slowed everything down and now it works. Hope this works for you.