2004 Grand Prix GT1
204,000 Miles
If the selector is set to 1 the car will accelerate slowly, and will reach 20 MPH at about 2500 RPM. If you press the gas too hard through 1st gear it will shudder a bit. If you then move the selector to 2 it will shift into 2nd gear and accelerate normally through 2nd. The sames goes from 2-3 and 3-4/D. If you leave the selector at 2, 3, or D and attempt to accelerate from a stop the car goes nowhere. It is my understanding that the selector is simply used to limit the car to a certain gear range, so 1 is 1st only, 2 is 1st and 2nd gear, and 3 is 1st, 2nd, and 3rd gear. The fact that it will only accelerate from a stop when limited to 1st gear seems odd to me. If it were stuck in limp mode it should still accelerate with D selected. It gives no indication that it's in limp mode, and when I hooked my code scanner up to it there were no codes pending or otherwise. I checked the transmission fluid and it seems to be a bit old, but is up to the max mark on the dipstick. I've heard that these transmissions have issues with the pressure control solenoid failing, and it wouldn't be the first time a part has failed or been failing without setting the check engine light. Any help would be appreciated.