Help with trouble codes

My sister got her 05 malibu a month or so ago and now the check engine light just came on. i dont know it it happened because it was the first time she used the remote starter but thats when the light came on.

trouble codes are P0128 and P0463. i know 1 has to do with her heat acting up. doesnt blow real hot but does work. the second has to do with the fuel level sending unit. it seems to be working fine tho, always shows where fuel is and doesnt move randomly so im lost with that one.

can anybody help me with these issues?

The most likely cause of the 128 is that it needs a thermostat. Won't cause driveability concerns, just the light is on and warmup may be slow since that is the code anyway.

I doubt that the fuel gauge is right either. The conditions of the code are that the pcm defaults the fuel gauge to empty, other than that it is a history code if the problem that set it is gone. Clear it and see if it comes back if the gauge is working right. I bet it needs a fuel level sensor before it is said and done. These cars, actually GM as a whole are good for that problem...

im going to change the thermostat when i get a chance. the fuel gauge works fine, it moves like its supposed to and always looks right when i put gas in. i hate her car, a new problem popped up right after i posted my first message.

i drove her car to make sure it was running fine. i stopped and put the car in park and when i went to put it in drive and it wouldnt move. kept trying and it finally went into drive but then i heard a "snap". it shifted fine but when i got home i parked and checked to make sure it shifted fine and it did. so i turn off the car and i cant remove the key from the ignition. it eventually came out but now the key wont go in the ignition at all....

anybody know what this could be?