How to fix the back seat release on my 2014 GMC Terrain

see your dealer

either debris or latch / linkage damage /disconnect crawl into back with a flashlight and long screwdriver remove the plug in rear panel and use screwdriver to move latch release

All of the functions on the seat are controlled by "one" fuse. Forward, back, up, down and recline, If one is inop. The whole seat bottom needs to be replaced. Now if you hear an audible bump noise when you rapidly flip the recline switch back and forth, you may be able to free it up by working it and see if that helps to free it up for sometime. When those motors sit in one position day after day month after month without being moved, they tend to "stick" but if you can't get it to free. The bottom of the seat will need to be replaced. Those are not cheap by no means and it would be a good idea to let a professional do it unless you are up to figuring out where all the brackets and nuts and bolts go and the proper wire routing because it is very tedious work. Not trying to scare you from doing the job but just stating a fact. But I hope you get the issue corrected. Jesus loves you, John 3:16-17 (KJV) :o)

the dealership apparently has a bulletin that came out in 2014 about the misfire issues and it said to replace both camshaftsensors.

Try this for the back seat: Pull the back seat down. Unscrew all the bolts behind the back seats to release it from the brace. Pull the seat back off the rear deck and out of the car. Feel under the seat cushions for release tabs on both sides. Pull the release tabs to loosen the seat cushion. Push the seat belt buckles into the holes to prevent the seat from getting caught up in the seat cushion

It shows P16A1 as throttle sensor with high voltage. Take to dealer or ? and they will change the sensor.

You paid for it, take it back. Don't let them get away from not fixing your truck.

There should be a button or lever at the base of the head rest. They are not always easy to see. It will either push or pull to release it.

Took mine to the dealer and they did an upgrade on the system ..fixed